NEAL: NERVOUS SYSTEM IN SQUALUS ACANTHIAS. 268 
homologized with the mouth of Ascidians? 2. Is it or is it not homol- 
ogous, either wholly or in part, with the mouth of Craniota? Upon the 
answer to the former question would seem to depend the settlement of 
the question whether the mouth of Amphioxus may or may not be re- 
garded as a visceral cleft, for there is no reason to believe that' the 
mouth of Ascidians represents a pair of visceral clefts. Notwithstanding 
that Willey appears to have in the asymmetrical mouth of Amphioxus 
strong evidence in favor of his homology, which has also met the 
approbation of Marshall (93), I consider the different relation of the 
Tunicate and Vertebrate mouth to the brain vesicle a very serious ob- 
jection to his theory. Furthermore, the presence of a preoral intestine 
in Vertebrates, which in Squalus extends (morphologically) anterior to 
the infundibulum, —even to the neuropore, as does the intestine of 
Tunicates, — leads me to agree with Beard, Kupffer (’88 and ’91), and 
van Wijhe (94), that in the present mouth of Vertebrates we have ¢ 
neostoma, and also that a palwostoma homologous with that of Tunicates 
must be sought in an anterior opening of the preoral intestine. Kupf- 
fer finds evidence of this paleostoma in the ectodermic invagination of 
the hypophysis towards the “ Preoraldarm,” while van Wijhe finds 
it in Amphioxus, as stated in the Table, in the actual opening of 
the preoral intestinal diverticulum of the left side as the preoral pit 
(Räderorgan). 
Waiving the question as to which, if either, of these theories is cor- 
rect, I regard the mouth of Ascidians as opening at the morphologically 
anterior end of the alimentary canal; for there ‘appears to me noth- 
ing in the literature upon Tunicates to show the presence of a preoral 
intestine in these forms. The mouth of Appendicularia, which has no 
“preoral lobe,” (though homologized by Willey with the preoral intes- 
tinal diverticula of Amphioxus and the premandibular cavities of Crani- 
ota,) has a terminal position.’ According to Willey the method of 
formation of the preoral lobe in those Ascidians possessing such is as 
follows (p. 218): “When the larva first hatches, the entoderm and 
ectoderm are in contact with one another at the anterior extremity of 
the body, just as they are in the earlier stages. Soon, however, the 
ectoderm, with the adhering papilla, springs away from the endoderm 
at this point, leaving a space into which the two lateral mesodermie 
1 Willey (’94, p. 277) writes: “ Whatever the truth may be as to the precise 
systematic position and phylogenetic value of Appendicularia, one thing, to my 
mind, remains absolutely certain, namely, that it has descended from a form which 
possessed a preoral lobe, and that it has secondarily lost that structure.” 
