xlvi Journal of Comparative Neurology. 



the writer's suggestion that "if neuromeres once existed in the fore- 

 brain they would be visible only at an early stage. . . The so-called 

 fore-brain neuromeres differ from those of the medulla in involving 

 only dorsal structures." He also apparently succeeds in resolving the 

 the discrepancies between Froriep's account and that of other writers. 



Fifteen pages are devoted to original observations on metamerism 

 in Acanthias and both descriptions and plates are admirably done. 

 Especial praise should be awarded the plate of photographs of the very 

 young stages which are particularly valuable, as also the dissections re- 

 produced in plate XXVIII. The constancy of the phenomena in ex- 

 tremely early stages in various groups serves to justify the present 

 writer's prediction and to furnish a new motive for a re-canvass of the 

 subject. The suggestion that they are artifacts is satisfactorily disposed 

 of, though it is less clear that the node-like structure sustains a positive 

 and constant relation to the definitive structure of the brain. Uo they 

 look backward rather than forward? 



This segmentation is said to be independent of mesodermic influ- 

 ence and, as proof of this, the fact is cited that it precedes the meso- 

 derm segments. It should be noted, however, that if it be conceded 

 that the segmentation is not due to direct mechanical influence and so 

 really has morphological significance, as the author claims, then we 

 must look for the cause in a state when the head was fully segmented 

 and mesodermic influence then could readily be appealed to. This the 

 author would doubtless agree to. 



In Squalus he recognizes as represented in the ontogeny at least 

 fourteen paired neural segments. The assignment of neuromeres to 

 the sense organs and nerves is as follows : 



.1 



I Mid-brain. 



Hind brain. 



I. Olfactory 



II. Optic. [- Fore-brain. 



III. Pineal sense organ 



IV. Oculo-motor. 

 V. Trochlearis. 



VI, "Anterior" (cephalic?) root of V. 



VII. Main root of V. 



VIII. No nerve. 



IX. Facialis. 



X. Auditory. 



XI. Glossopharyngeal. 



XII. ] I 



XIII. I Vagus. J 



XIV. I 



The segments are serially homologous. In Squalus the optic vesi- 

 cles are the first rudiments of sense-organs to appear and originate be- 

 fore the separation of the fore-brain. Their peculiar form has led to 



