REIGHARD ON THE HEAD CAVITY OF THE ELASMOBRANCHS. 81 



attached to the male by means of the adhesive organ. During the past 

 season the writer has carefully watched the young fish in a number 

 of nests and has visited the nests daily in order to see when and bj 

 what means the young fish leave the nest. As a result of these observa- 

 tions it may be stated positively that the young fish do not leave the 

 nest until they have learned to swim independently and not until the 

 adhesive organ has been absorbed. They then leave the nest in a swarm 

 wuth the male and remain in shallow icater in the vicinity of the nest 

 for some days. As the young increase in strength the range of the 

 swarms becomes greater and they are found at increasing distances 

 from the original nest, which becomes obliterated. The young fish con- 

 tinue with the male and in shallow^ water until they are between eighty 

 and ninety millimeters (about three and one-half inches) long. At this 

 time they have acquired the brilliant larval coloration and are ex- 

 tremely active. The writer has not seen fish of larger size in swarms 

 or attended bv the male. 



ON THE ANTERIOR PIEAD CAVITY OF THE ELASMOBRANCHS. 



JACOB REIGHARD. 



(Abstract.) 



It was shown that the anterior head cavity of the Elasmobranchs is 

 exactly comparable to the adhesive organ of Amia. The two structures 

 originate in the same region and in the same manner. Both subse- 

 quently degenerate. 



In view of this fact the anterior head cavity of the Elasmobranchs 

 was interpreted as an aborted adhesive organ. The view was expressed 

 that this structure, which is incapable of supporting a heavy weight, 

 had been rendered useless to the Elasmobranch embryo by reason of 

 the accumulation of yolk in the eggs of the members of that group. 

 The organ had consequently degenerated. If this interpretation be 

 accepted it follows that the Elasmobranch and Ganoid lines must have 

 separated before the accumulation of yolk in the eggs of the former. 

 In other words the persistence of an adhesive organ in the Ganoids is 

 evidence that these forms never possessed a large amount of food yolk 

 such as now occurs in Elasmobranchs. 

 n 



