736 



as ill the adult fishes. He found both (the doi^al and the ventral) 

 simultaneously in the suuie animal, in tlie forms which now-a-dayb, 

 after Tate Rkgan. are called Galeoidei. In ra_> s on the contrary, onI\' 

 the ventral diverticulum of the examined fishes : Raja, Torpedo, Trygoii 

 and Myliobatis was found to be present. Tlie dorsal one was absent 

 in concurrence with the results of Joh. Müllüh, who found it in 

 rays only in the family of the Rliinobalidae. 



Vice versa the ventral diveiticulum was foun<i missing, wiiile only 

 the dorsal one was present in Acanlhias and Heptanchus; each of 

 which is a representative lesp. of the groups Squaloidei and 

 Notidanoidei. 



On the ventral diverticulum a follicle, resembling an oval bladder, 

 develops in all forms which possess il. It nearly touches the auditary 

 labyrinth, is lined on the inside with columnai' epithelium, and is 

 connected to the wall of the spiracle by a pedicle, which may, or 

 niay not have a lumen. In an adult Torpedo the bladder was found 

 to be very large. 



As regards the morphological significance of the follicle, van Bem- 

 MEi,EN thought of the probability of a homologue with the supra- 

 pericardial body, which primarily is also a single little bladder. He 

 says (I.e. p. 178) "[s|)ater] tritt aber der grosse Unterschied ein : 

 die Su|)rapericardiall<öi'|)er entwickeln sich zii diiisenai tigen Geliilden ') 

 die Spritzlochblclschen treiben iiitr eine oder zwei atMiiöse x'^iisslüi- 

 pungen oder bleiben wohl ganz einfach." 



Van Biommklen further thouglit of the probability of considering 

 the follicle, e\en as the suprapericardial body, as Ihc remains of an 

 original gill cleft. 



My opinion is that this conception cannol be adhered to any 

 longer, and that the follicle is a spiracnlar sense oigaii bladder. 



Van Bemmelen did not consider this possibility, liecaii.se he had 

 evidently not observed a supplying nerve. 



No mention is made of the appearance of a tollicle from the 

 dorsal protrusion of the spiracle in the Galeodei. We may thus 

 accept that il is absent there. 



Acanlhias and Heptanchus only show the 'tlorsal protrusion. Is 

 the spiracular sense organ now also found missing in them or not? 



Van Bemmei.en speaks of a "dorsale Ausslülpung". but also calls 

 it an "Anliang" of the spiracle. He says: (I.e. p. 176). "Bei erwach- 

 senen Exemplaren von Acanthias endlich konnle ich den Anliang 



'i Tlieir structure in the Selachianp. tlien has much in common with that of thn 

 thyroid glaiul, from which Ihey, tiowever. totully clilTer morphologically. 



