202 bulletin: museum of comparative zoology. 



and it may also be inferi-ed that the median portion of the connect- 

 ing stalk is morphologically the undifferentiated anterior portion of 

 the chorda, while the more lateral portions of the connecting stalk 

 may be regarded, as they have been by Killian ('91, p. 102), as 

 representing the sclerotome of the somite. Furthermore, the inference 

 drawn by Froriep ('92*), on the ground of evidence pi-esented by 

 Kastschenko ('88) and Kupflfer ('88, '90, '94), that the lumen of the 

 connecting stalk mast be ventral and morphologically a part of the 

 proca'lom, receives no support. If Kupfter's statement that the pre- 

 mandibular cavities of Ammocoetes are formed as diverticula from the 

 alimentary canal is correct, their development in Ammocoetes must 

 differ essentially from that in Squalus. Goette ('90), however, flatly 

 contradicts Kupffer's statements. My own observations on Ammocoetes 

 lead me unhesitatingly to accept the evidence presented by Goette.^ 

 Besides, the criteria furnished by the study of the early stages of devel- 

 opment of the premandibular cavity in Squalus seem to me more satis- 

 factory, because more decisive, than the evidence used by Ivupffer ('93% 

 p. 522) to demonstrate the ventral nature of the connecting stalk of 

 the premandibular cavities in Ammocoetes, viz. the relation to a blood- 

 vessel which is only hypothetically the complete homologue of the dorsal 

 aorta. I find this blood-vessel in embryos of Ammocoetes of somewhat 

 advanced stages of development (4 mm.) extending above the connecting 

 stalk of the premandibular cavities, as the apparent anterior continuation 

 of the dorsal aorta, as stated by Kupffer. But there is also ventral to 

 the connecting stalk a similar blood-vessel, wliich unites with the dorsal 

 vessel both anterior and posterior to the connecting stalk. It is conse- 

 quently difficult for me to comprehend why the more dorsal vessel rather 

 than the more ventral one is to be regarded as the anterior continuation of 

 the dorsal aorta. Kupffer gives no reasons, simply stating that the ven- 

 tral vessel can be homologized, if at all, with the carotis ventralis of Mam- 

 malia. Now, if we are to apply rigidly such a criterion as Kupffer's to 



am unable to accept IIoEfmann's conclusion on the basis of the evidence he pre- 

 sents, I believe there are good grounds for holding that a visceral arch, which 

 once existed between the mandibular and the hyoid (first and second visceral) 

 arches, has disappeared in phylogeny. The evidence in favor of this view will bo 

 summarized later. 



1 That Kupffer has not in his studies come to a right understanding of the 

 development of the anterior head mesoderm seems to me certain from a comparison 

 of my sections with those figured by him ('90, Figg. 31 und 32, Taf. 28). The 

 cells which he calls ganglionic are in my opinion the anterior mesoderm. This 

 appears to me to be Kupffer's fundamental error. 



