The Embryology of Heterodontus japonicus 7l7 



capsules with a slimy coating are those recently deposited, and the degree of sliminess 

 lessens perceptibly during the first days and weeks. The capsule then acquires a smooth 

 but elastic surface; the spiral band is thick and rubber-like. In later stages the capsule be' 

 comes rougher in texture, thinner and more brittle; its upper and lower edges become 

 frayed, and its lateral band is apt to be imperfect. On its surface various foreign growths 

 appear: bryozoa and barnacles especially. 



When capsules were opened and kept in aquaria, the young (still within the capsules) 

 lived for some time. Early stages were kept alive for several days, especially if well- 

 covered with albumen; later stages lived for weeks. Death in such cases results ultimately 

 from invasion of bacteria and infusoria: these attack the yolk, causing it to soften in spots 

 and finally to break down. 



Several times. Dean obtained gravid females; but he never found eggs whose capsules 

 were in an early stage of formation. The adult Heterodontus japonicus is not often taken. 

 It rarely is caught in seines, probably because it occurs in regions where rocks are abundant 

 and where a seine is not likely to be drawn. Even when netted, it is rarely retained, for 

 it is not marketable (see also pages 688 and 694). Since it was found impracticable to 

 secure a large supply of spawning fish, the stages of fertiliziation and beginning cleavage 

 were not obtained. These stages doubtless occur during the descent of the egg and its 

 enclosure in the capsule. The earliest embryonic stages studied by Dean were fairly 

 early (but not the earliest) cleavage stages (Figures 7 and 8, plate I). These were eggs 

 already in capsules which were practically completed, and were soon to be deposited. 

 Dean states that the egg is in a blastula stage at the time of deposition. 



Heterodontus japonicus, like H. pMlipi, is oviparous and not ovoviviparous. In both 

 species, the earliest stages of cleavage occur while the egg is still in the oviduct. 



EMBRYONIC DEVELOPMENT OF HETERODONTUS JAPONICUS 



As the title of this article indicates, we are here concerned primarily with the em- 

 bryology of the Japanese Bullhead Shark, as set forth in Dean's notes and drawings; but 

 the observations of other authors, working mainly with H. phillipi or with H. japonicus, 

 will be noted for comparison. It will be evident that descriptions of the development of 

 H. pMlipi are confined to the early stages; while practically all that is known concerning 

 the embryology of Heterodontus japonicus has been either discovered by Dean or made 

 possible by his labors. 



RATE OF EMBRYONIC DEVELOPMENT 



Under "Breeding Seasons", I have already recorded observations to the effect that 

 eggs of H. phillipi in blastula and gastrula stages are abundant in August and September 

 (spring months in the southern hemisphere) and that hatching has been observed in 

 May. In the absence of more adequate data, this indicates a probable duration of nine 

 months for embryonic development. Whitley (1940) states that the period of incubation 

 for H. galeatus is "at least five months". 



