The Embryology of Heterodontus japonicus 709 



While the embryo of H. japonicus is developing, the capsule undergoes steady 

 deterioration, as in Chimaera (Dean, 1906) and in other elasmobranchs. The substance of 

 the capsule becomes thinner, more ''tense" and fragile. An arrangement is also developed 

 which enables the young fish to carry on respiration. At either side of the upper or 

 larger end of the capsule, near the line of junction of each marginal band, there is a deep 

 infolding in the wall (as indicated by the arrow in Figure 76, plate VII) . Later, by a process 

 of weathering, this respiratory groove opens and widens as a slit (Text'figure 59, page 752). 

 (A respiratory slit of this kind in the eggs of elasmobranchs appears first to have been 

 mentioned, though hardly described, by Home, 1810, page 213). In addition, similar 

 respiratory slits appear at the "lower" or more pointed end of the capsule. 



The upper slits in the egg capsule of H. japonicus play an active role in the process 

 of hatching, which is described by Dean as follows : 



By a continuation of the process of weathering, the upper slit comes to open not only in 

 its lower portion (i.e., in the direction of the contained egg) but in an extended line along 

 the upper and median margin [of capsule] . By this process the entire chisel-like rim of the 

 capsule finally weathers open, and its sides separate, leaving a slit between. This follows 

 the absorption of the hard wedge of albumen which has from the beginning blocked up the 

 large end of the capsule. Old capsules, it was observed, are "tense", and hatching occurs, 

 with a rapidity which reminds one of the dehiscence of certain seed pods. The sides of the 

 terminal aperture open and shut in a twinkling, and one is given the impression that the 

 young fish is shot out of the capsule. There is a writhing on the part of the imprisoned fish, 

 and it emerges with a rapidity which quite disconcerts the observer if, as in my own experience, 

 he happens to be holding the egg capsule in his hand. [For further details, see page 753] . 



Among the capsules which passed through Dean's hands, there were several which 

 were newly deposited and perfect except that none contained an egg. Such empty 

 capsules are called "wind eggs". Externally, these capsules were quite indistinguishable 

 from the others, except by their lighter weight. Dean assumed that they resulted from 

 unilateral ovulation, during which the oviduct of the side opposite to the gravid one was 

 stimulated to produce a capsule. 



HABITS OF HETERODOKTUS 



In this section, and in those that follow, we are concerned primarily with the 

 Japanese species, Heterodontus japonicus; but reference will be made to other species 

 wherever information is available. 



HABITAT AND GENERAL HABITS 



There is a curious lack of information concerning the depths at which adults of some 

 species of Heterodontus have been taken, though depths at which the eggs of one of 

 these species have been found are recorded in a later section of this article. Osburn and 

 Nichols (1916) record the capture of a specimen of Gyropleurodus (Heterodontus) francisci 

 8 inches long, dredged from 13 fathoms of water, in Magdalena Bay, Lower California. 



