The Embryology of Heterodontus japonicus 



705 



thus described is the one represented in Text'figure 35. Dean states that though several 

 gravid sharks yielded each but a single encapsuled egg, in each case the condition of the 

 "opposite" ovary indicated that another egg had already been laid. These observations 

 support the data recorded in the section on ''Egg-laying Habits", and indicate that two 

 eggs are laid at about the same time. We also infer that occasionally both ovaries are 

 functional at the same time. From Text-figure 35 it appears that the "uteri" of both 

 sides are well developed. 



THE EGG CAPSULE: ITS STRUCTURE AND FUNCTIONS 



The earliest published drawings of the egg capsule of Heterodontus pMlipi are 

 those of Dumeril (1865), reproduced as my Text-figures 36a and 36b. These drawings 

 have been extensively copied, but Waite (1896) states that they are not very good, being 

 doubtless drawn from dry and distorted specimens. The frayed condition at the apices of 

 the two spiral appendages is an artifact. McCoy (1890) contributed a drawing that 

 differs from DumeriPs in that the apices of the two spiral appendages are blunt and are 

 not frayed. McCoy states that these 

 "eggs" (capsules) are conical in shape, 

 about six inches long, and surrounded with 

 two broad keels extending spirally and 

 obliquely round the egg from one end to 

 the other, like six turns of a broad screw; 

 the substance is of a tough, dark-brown, 

 horny appearance. 



A suggestion as to the advantage of 

 the peculiar form of the Heterodontid egg 

 is offered by Allen (1892) as follows: 



That well-known frequenter of Aus- 

 tralian harbours, the Port Jackson Shark, 

 lays a pear-shaped egg, with a sort of spiral 

 staircase of leathery ridges winding around 

 it outside, Chinese pagoda-wise, so that 

 even if you bite it (I speak in the person of 

 a predaceous fish) it eludes your teeth, and 

 goes dodging off screw-fashion into the 

 water beyond. There's no getting at this 

 evasive body anywhere; when you think 

 you have it, it wriggles away sideways and 

 refuses to give any hold for jaws or palate. 

 In fact, a more slippery or guileful egg was 

 never yet devised by nature's unconscious 

 ingenuity. 



Text-figure 36. 



Egg case of the Port Jackson shark, Heterodontus 



phillipi: A, entire specimen; B, egg case with interior 



exposed. According to Dumeril the egg case is about 



130 mm. (5.1 inches) long. 



After Dumeril, 1865, Atlas, Figs. 2 and 3, pi. 8. 



