The part five of this article contains descriptions of life colors of ten species (nos. 77-86) of the Apodes found in Suruga Bay. The interesting species are as follows: Ophichthus urolophus, O. roseus, Gymnothorax leucostigma, etc. The remaining species of the Apodes, with some exceptions, found in this bay were already mentioned their life colors in several zoological or ichthiological publications in Japan.
(i) The morphology and histology of the gill filaments of Mastacembelus armatus are described. (ii) Chloride secreting cells are absent in the branchial epithelium. (iii) The intra-epithelial branchial glands are the mucous cells. (iv) COPELAND, KEYS and WILLMER and others have described certain cells in respiratory (branchial) epithelium of fishes which appear in fishes adapted to different osmotic environments. The fact, however, that BEVELANDER, the author and others, have described only mucous cells in this environment, and the very great possibility that mucus is concerned with ionic transfer suggests that chloride and other ionic transfer effected by the branchial epithelium is mediated by mucous cells.
For distinguishing cyprinid fish from catostomids, Hums and LAGLER (1947) have offered a general standard as cited in the present paper (p.164). However, their belief on morphological law on anal fin will be confined to American freshwater fish. If their, law is adopted to the classification of our Japanese cyprinid fish (46 speices in 27 genera), it seems illogical to find that most of the bottom dwellers referred to Gobioninae in our water falls within the same category as catostomid fish. This fact alone will lead us to believe the law proposed by the above two workers based on general relation between the mode of living and proportional length of body parts, but not on a fact more deeply rooted. It is worthy of notice that Gobioninae falling in the category of sucker circumscribed by this law have sucking lips without exception, and in their external appearance our gobionine fish have much higher resemblance to Catostomidae than other Cyprinidae of Japan. The phenomenon seems to suggest that the family of sucker have radiated adapting themselves to North American waters, and one or two species in Asia, while far greater number of Cyprinidae have evolved in the old-world. In other words, some cyprinid fish of the old-world, say Gobioninae, corresponding to sucker in the new-world, have occupied bottom layer as their normal niche just as the catostomid fish done in America. The writer considered that the phenomenon as such may safely be interpreted as an example of ‘parallelism’ in evolution discipline which is generally accepted.