264 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
bands force their way. In this way a special anterior portion of the 
body cavity, preoral and preenteric, is produced, and is at first com- 
pletely filled by a compact mass of rounded cells derived from the meso- 
dermic bands. . . . The anterior, or preoral portion of the body cavity, 
of which we have just traced the origin, is, and subsequently becomes in 
a still more pronounced way, the cavity of the snout, or preoral lobe.” 
On the other hand, the preoral “head cavities” of Amphioxus, which 
Willey homologizes with the “preoral lobe” of Ascidian larvee, are formed, 
as stated by Hatschek (81), from an abstricted portion of the preoral 
archenteron. ‘The differences in the formation of these two structures, 
therefore, seem too striking to permit their being considered completely 
homologous with each other. 
Evidence has already been given in this paper which, in my opinion, 
makes it impossible to homologize the preoral “head cavities” (anterior 
entodermic diverticula) of Amphioxus with the “ premandibular head 
cavities” of Craniota. The morphologically anterior portion of the arch- 
enteron, the “anterior head cavities” (Platt), are the only structures 
in higher Vertebrates which, in my opinic ı, can be homologized with 
the “head cavities” of Amphioxus. Homo-ogizing, therefore, the “ an- 
terior head cavities” in these two forms, I submit on the opposite page 
for comparison with Squalus the table of the anterior eleven segments 
in Amphioxus as I interpret them. 
If we compare Tables III. (p. 253) and V., we find the following 
fundamental resemblances in the segments of Squalus and Amphioxus. 
Of the component elements of the first segment, that which I have 
regarded as the somatic element, consists of paired cavities cut off from 
the anterior portion of the archenteron. Since in both cases these 
cavities represent ventral as well as dorsal and lateral portions of the 
archenteron, it is impossible to contend that they contain only the 
mesodermic element of the segment. It seems not improbable that 
potentially they represent also the visceral-pouch element between this 
and the following segment. The opening of the left of these in Amphi- 
oxus to the exterior as the preoral pit may be regarded as evidence 
favoring this view. Moreover, M. Fiirbringer (97, p. 633) finds a late 
differentiated and rudimentary myotome, which lies anterior te the 
dorsal paired nerves II, which would, if present as stated by! epre- 
sent the mesodermic element of this segment, and the “auterior head 
cavities” would in consequence necessarily be regarded as modified or 
abortive visceral pouches, as held by Kupffer. Since my sections of 
Amphioxus give me no evidence of this rudimentary myotome, I hold 
