Two general frames of mind seem to exist in the study of ostracods. In one, the intent has been to understand the taxonomic group. Biologists and paleontologists in this cate gory have been called ostracodologists. In the other category are those who may treat the ostracods as experimental animals, simply because they are more useful than other groups of organisms for the study of a particular basic problem in biology. In reality, however, systematists' minds seem to go to and fro between the above two frames, perhaps because, if one tries to utilize ostracods as experimental animals, then one is best advised to know them as well as the ostracodologists do (cf. Ray, 1960).

In systematic studies ostracods have three advantages. The first is that they are among the most common marine metazoans found in shallow seas, and, therefore, micro geographic distributions and population structures are relatively easy to detect and to analyze. The second advantage is that certain groups of ostracods, especially the crythe raceans, have calcareous exoskeletons with complicated morphological characters. These include several of relatively low phenotypic variability, as exemplified by the spatial patterns of organules for precisely placed pore canal openings. Carapaces with these polygenic characters, which are generally consistent with the deductive taxonomic conclusions derived from the analysis of "soft parts" such as appendage structure, are resistant to destruction after the death of the animal and are therefore abundant as fossils. This second point is especially important with respect to progress in the study of ostra- cod genetics, because most groups of organisms which have been studied extensively in the field of genetics have extremely poor or even no representation as fossils. The third point is that many of the shallow marine ostracods are relatively easy to culture, even using the well-known and simple petri-dish technique.

Ostracod species chosen for culturing should preferably be: (1) ubiquitous, obtainable at any season of the year and at many places along the coast; (2) tolerant, standing up to wide ranges of environmental fluctuations, especially in temperature, salinity, concentration of detrimental materials (e.g., metallic ions), and to bacterial conamination; (3) easy to feed; and (4) those which reproduce easily and brood their young within the carapace, thereby protecting larval development (cf. Ray, 1960). Some benthic and intertidal species (e.g., Neonesidea oligodentata and Xestoleberis hanaii) seem to satisfy most of the above qualifications. Other promising benthic species living below the low tide line of the inner bay are Aurila punctata, Loxoconcha (Loxoconcha) laeta, and Ruggieria (Keijella) bisanensis. The former two species crawl on the leaves of Zostera which grows on sandy bottoms, and the last crawls just below the sediment-water inter face in areas with shallow mud bottoms. In contrast to the above examples, some species (e.g., Vargula hilgendorfii) which are sensitive to sea water pollution are difficult to keep for long periods under laboratory conditions.

Accurate observation throughout the entire life cycle perhaps should be one of the first steps in the detailed systematic study of Japanese ostracods, as our knowledge of their life histories consists so far of only a patchwork of fragmentary observations. Another unexplored but important and promising field which can be investigated through the culturing of ostracods is the study of polymorphism. In fact, two types of polychromatism can be observed among the above shallow water species. One occurs in the chromatophore pigmentation exemplified by the black and grey forms of Loxo concha (Loxoconcha) laeta and of Hemicytherura sp.; the other occurs in the color patterning seen in Neonesidea oligodentata and in Paradoxostoma sp. In the former case, the difference between the two forms may be seen in the carapace ornamentation as well. Cross-breeding is necessary to test the genetic relations of these phenotypic varieties, for it is highly likely that some of these varieties may turn out to be examples of genetic polymorphism, as a number of copepod and isopod crustaceans have.

An interesting problem to investigate at the chromosome level is the development of paired forms, especially in cytheracean ostracods. Such a pair would consist of a northern cold-water form and a southern warm-water form. In the seas surrounding Japan they are observed to have either allopatric or partially sympatric distribution patterns. Both forms have the same morphology, but the northern forms generally are larger and thin shelled in comparison with the southern forms. The fundamental patterns of ornamentation and of shell structure are very similar and suggest very close relationships between the two forms. Differences do exist, for example in the normal pore canal distributions, but at present it is still difficult to determine the precise nature of these structural differences. The difference in size may be explained by the occurrence of polyploidy or polyteny in the northern forms, as was found in some copepod crustaceans (McLaren, Woods and Shea, 1966). The following pairs are the examples of northern and southern forms: Cythere lutea uranipponica-C. 1. omotenipponica, Schizocythere okhotskensis- S. kishinouyei, Paradoxostoma brunneum brunneum-P. b. brunneatum. Except for Para doxostoma, whose carapaces easily disintegrate soon after death, it should be possible to trace the fossil records of these species in the Japanese Neogene formations.

It is relatively easy to extrapolate biological theories (e.g., the theory of speciation) speculatively into the geologic past, but it is difficult, if not impossible, to elucidate with fossil evidence the paleobiologically significant historical events, which may be complicated but which may be interpreted in terms of biological theories. It may also be true that cladogenesis is not so simple as the analogy of a branching tree. The phylo genetic tree is convenient for summarizing the inferred evolutionary histories of groups of organisms in higher taxonomic categories. However, it may be more injurious than beneficial for illustrating the relationships of descendants at the intraspecific and inter specific levels, in that it conceals the dynamics of speciation in the dendritic expressions. Whether speciation be allopatric, or parapatric, or even sympatric, studies of the geo- graphic distribution of intraspecific variation and interspecific differences covering the entire area of species distribution, rather than just of overall or local morphological variations, will become relatively more important as a function of time for paleo biological investigation at these levels of organization.

The Japanese Islands extend from latitude 46°N to 24°N and fall within an area which underwent considerable paleogeographic and paleo-oceanographic changes during the Neogene. For example, during the late Miocene, the boundary between the cold and warm climatic zones shifted southward from Hokkaido to near its present position. During the Pleistocene, the geographic gradients of water temperature at this boundary may have been either steep (during glacial periods) or gentle (during interglacial periods) along the Pacific and Japan Sea coasts. The northern and southern margins of the areas of survival and reproduction for thermophilic and cryophilic species, respectively, would certainly have oscillated along with these fluctuations in water temperatures (cf. Hazel, 1970). But some species might have developed step clines or peripheral isolates and their drawbacks. Both the abundant fossil records and the reasonably good understanding of the Japanese Neogene paleogeography may furnish an excellent setting for tracing the history of certain species of ostracods which have survived these fluctuations of the steep temperature gradients.

To cite an example of a cold water species, Cythere lutea, which populates subfrigid to mild temperate climatic zones in both the Atlantic and the Pacific Oceans, has extended its distribution southward into the warm temperate climatic zone along the Pacific coast of Japan. This may have resulted in the development of a new form which has been called Cythere lutea omotenipponica. It is also interesting to note that some species of living warm water ostracods (e.g., Hemicytherura kajiyamai, Aurila sp., Schizo cythere kishinouyei), which first settled in Japan in the middle Miocene, have maintained a status quo in phenotype up to the present. They may have been aided by an unchanging ecology and homeostatic mechanisms. New appreciation of the significance of homeo stasis may be gained as we learn about long periods of time during which populations have had several opportunities to interbreed through changes in paleogeography. The evolutionary transition of Schizocythere from the Paleogene-type ornamentation to that of the Neogene-type through the Oligocene-Lower Miocene regression is another interesting problem, but it may need to be studied on a world-wide scale and with a strongly geological approach.

Few investigations of Japanese pre-Miocene ostracods have yet been made. In fact we know almost nothing about the stratigraphic and geographic distribution of Japanese Paleozoic, Mesozoic, and Paleogene ostracod species. However, the abundant Paleozoic ostracods in Japanese limestones and the well-preserved Upper Cretaceous and Paleo gene ostracods, especially from Hokkaido, will provide excellent materials for paleobio logical studies. Both occur in areas which have already been accurately mapped using the zoning of fusulinaceans and conodonts (for Paleozoic formations) and ammonites and foraminifers (for Upper Cretaceous and Paleogene formations).

We believe that the Survey for making a checklist should not be confined to a mere compilation of present taxonomic knowledge. It should also serve as a starting point for understanding "the pathways and causations responsible for evolutionary changes" (Mayr, 1969, p. 2).