J 



714 



Bashford Dean Memorial Volume 



Text-figure 41. 

 Ventral view of the pelvic region of a female Heterodontus japonicus showing a series of stages (A to D) in the 

 process of extrusion of the encapsuled egg. In A, the cloacal region is shown between the pelvic fins, but the 

 extrusion of the egg has not commenced. In D, the dotted lines represent portions of the egg case still within 



the body of the mother. 



From drawing left by Bashford Dean. 



extrusion the capsule rotated about its long axis as though it had been unscrewed. 

 Evidently this was not the only occasion when Dean saw an egg protruding from the 

 cloacal aperture of one of these sharks, for on the margin of his drawing reproduced as 

 my Text'figure 41d there was found a penciled note in Dean's handwriting: "Sometimes 

 4 ridges show". 



Dean thought that, in the case just described, the final extrusion of the capsule was 

 hastened by unskillful handling of the fish. But he notes that there are several considera' 

 tions indicating that the sudden extrusion of the capsule, which he observed, may have 

 been like the normal process of deposition. The capsule at this stage is very slimy. The 

 shark exercises a voluntary control over the sphincters of the oviducal apertures. It can 

 tighten or loosen its hold on the capsule, and it may even envelop the entire cloacal region 

 with the bases of the pelvic fins. The very suddenness of the process may have a distinct 

 advantage to the fish, for by it the capsule, on account of its peculiar form, is caused to 

 rotate — a motion which would obviously project it downward and backward in a straight 

 line, making it less subject to deflection by water currents. 



Eggs Found in Nests. — Of special interest is Dean's account of the occurrence 

 of the eggs of Heterodontus japonicus in "nests'" on the sea bottom: 



It is well known by the fishermen that the eggs of "Nekosame" are found among rock 

 fragments. On sandy bottom and in weedy reaches they rarely occur. The professional divers 

 (with suits) whom I employed to search for these eggs in the neighborhood of Misaki examined 

 carefully various kinds of bottom in water from three to eight fathoms, but without success, 

 for at that time we had not discovered where the eggs are usually located. For this discovery 

 I was indebted to the fishermen who dive for Haliotis, and from them I learned that the eggs 

 of Cestracion {Heterodontus) occur in "nests". An instance of their mode of occurrence may 

 be cited. 



