February 2, 1900.] 



SCIENCE. 



169 



in this region is sharply separable from the 

 cerebro-spinal, and there is no evidence that 

 the facial ganglion is in process of trans- 

 formation into a sjTnpathetic ganglion. In 

 Amiurus the geniculate is much larger and 

 crowded still more closely up to the Gas- 

 serian. It can however be clearly shown 

 that the r. lateralis accessorius in both 

 Gadus and Amiurus is composed mainly of 

 communis fibers and receives no fibers from 

 the Gasserian ganglion. 



From these results, and those of Strong, 

 Kingsbury and others, it appears that the 

 peripheral nervous system of Menidia pre- 

 sents us with a paradigm applicable in the 

 broad view to the Ichthyopsida as a whole. 



The Teleost gastrula and its modifioations : F. 



B. SUMNEE. 



The prevailing view that the germ-ring 

 alone furnishes the mesoderm and the ento- 

 derm must be revised, as well as the view 

 that in teleosts, the periphery of the plasto- 

 derm represents the whole blastopore. 



A specialized portion of the blastopore 

 occurs at the posterior end of the embryonic 

 shield a little anterior to the margin. In 

 Murcena and probably some other fishes, this 

 takes the form of an 6pen invagination of the 

 ' Deckschicht.' The cell thus invagina- 

 ted becomes the gut hypoblast. The cavity 

 persists for a while as that of Kupffer's 

 vesicle. Thus Kupfifer'^ original account, 

 written in 1868, was very near the truth, 

 although ignored or rejected by most of his 

 successors. 



In the cat-fish, trout and some others this 

 blind sac is replaced by a solid ingrowth, 

 such as Kowalewski described for the gold- 

 fish. Kupffer's vesicle is formed in this 

 mass of cells which, in the trout, at least, 

 probably furnishes the whole gut epithe- 

 lium. 



Iq the case of Scorpcena and probably 

 many other pelagic fish eggs, this reduction 

 has still further progressed, and we find at 



the posterior middle point of the blasto- 

 derm a small nodule of cells, causing a 

 thickening of the ' Deckschicht.' 



The present writer finds a condition in 

 Amia quite comparable to that in Murcena. 

 Although the egg of the former is holoblas- 

 tic, its gastrula is very like that of the Te- 

 leosts and far different from that of the 

 Amphibia. Dean has already pointed out 

 in Amia the homologue of Kupffer's vesicle. 

 The present writer also finds a rudimen- 

 tary syncytium or periblast with giant nu- 

 clei. 



On the embryology and phylogeny of Chimcera : 



Bashford Dean. 



The embryology of a chimseroid throws 

 interesting light on the relations of this 

 doubtful group. By this means the char- 

 acteristic structures of Holocephali are 

 shown to have arisen from distinctly Sela- 

 chian conditions: the palato- quadrate in 

 Chimcera colliei is thus early separate from 

 the cranium : the frontal clasperis to be re- 

 garded as the homologue of a spine of first 

 dorsal fin, which in ontogeny, owing to the 

 precocious growth of the enormous eyes, 

 shifts into its anterior position : the dental 

 plates arise from separate anlagen, which 

 in general are in the adulb represented by 

 the tritoral areas. 



C. colliei spawns near Monterey, Cali- 

 fornia, throughout the entire year, in deeper 

 water (about 75 fathoms, sp. gr. 1.027, 55° 

 F.). It deposits two eggs almost simulta- 

 neously. First cleavage about 26 hours 

 after egg is deposited : early cleavages sep- 

 arated by intervals of from 3 to 6 hours. 

 The young escapes from the egg-case in 

 about 250 days. Polyspermy occurs. Blas- 

 tula and gastrula distinctly shark-like. 

 Early embryo with broad medullary folds. 

 After closure of folds embryo differentiates 

 as chimseroid. Eye increases enormously 

 in size, altering the shape of the head, and 

 accompanies ventral displacement and ob- 



