92 ALUS. [Vol. II. 



internal to the parietal bone, while in Scomber they lie exter- 

 nal both to that bone and to the frontal. This seems to indi- 

 cate that Amia and Scomber represent separate lines of descent 

 from some fish in which the trunk muscles had not as yet in- 

 vaded the temporal part of the skull to the extent they have in 

 these two fishes. In Scomber, the muscles extend farther forward 

 than they do in Amia. If, then, there are in Scomber two less 

 anterior myomeres than there are in Amia, and the anterior seg- 

 ments in both fishes are in process of reduction, what is the 

 explanation of this independent and apparently aggressive activ- 

 ity in the muscles t 



Furthermore, aside from the fact that the last spino-occipital 

 nerve perforates the occipitale laterale, I find no indication what- 

 ever, in the skull of Scomber, of the incorporation in it of either 

 of the two occipital vertebrae of Amia ; and the simple fact 

 that this nerve is incorporated in the occipital part of the skull 

 is not necessarily any indication whatever, in any fish, of its 

 being a spino-occipital rather than a post-occipital one. 



My work thus leads me to conclude, not only that the spino- 

 occipital and first free spinal nerves in Scomber and Amia are 

 homologous structures, but also that the first two free vertebrae 

 of Scomber are represented in Amia by the two incompletely 

 incorporated occipital vertebrae. In this my conclusions are 

 directly opposed to those arrived at by both Sagemehl and Fiir- 

 bringer in their comparisons of Amia with other teleosts. 



Sewertzoff (No. 7, p. 240), in his examination of the skull of 

 Amia, simply confirms Sagemehl's earlier observations ; that 

 is, he finds three spino-occipital nerves instead of four. In 

 Lepidosteus osseus, he says (No. 7, p. 238) that Balfour and 

 Parker's investigations show that the myotomes in embryos of 

 that fish extend forward to the ear capsule, exactly as his own 

 investigations show that they do in embryos of Acipenser ruthe- 

 nus. In the adult Lepidosteus, he finds on each side of the 

 head, in addition to the two foramina said to have been previ- 

 ously described by Gegenbaur, a third and more posterior one 

 which "durch eine enge Ritze, wie durch einen Riss mit dem 

 hinteren Rande des Bogens verbunden ist " (No. 7, p. 239). 

 The anterior of these three foramina perforates the occipitale 



