346 Robert J. Terry. 



Dexter ('02),' in his study of the development of the paraphysis 

 in the fowl, has identified and figured subdivisions of the fore- 

 brain roof, comparable with those described by Minot ; and Warren 

 ('05), who has found the arches in Necturus, has shown a very 

 striking resemblance between the embryonic pineal regions of this 

 amphibian and Acanthias. 



In regard to teleosts it is probable that Minot's subdivisions of 

 the embryonic fore-brain are present throughout the class. In 

 Kupffer's ('06) figure of a trout embryo of 53 days, the epiphysis is 

 represented as an elongate evagination, but the other subdivisions 

 of the the roof are shown to have the form of arches and inter- 

 vening folds. A post-velar arch and the invaginations of the 

 velum and the posterior commissure are shown in Hill's ('94) 

 figure of Salmo fontinalis of 42 days. Opsanus embryos present 

 the six snjbdivisions and also a pars intercalaris. The intercalated 

 part first appears as a distinct segment in embryos of 3.5 mm. 

 lying between the posterior commissure and the epiphyseal arch. 

 As the result of forward growth of the commissure over the inter- 

 calated part, the latter as such disappears; that is to say, it no 

 longer remains a segment interposed between the posterior com- 

 missure and the epiphysis. It can be recognized, however, in all 

 later stages in the stretch of ependyma underlying the anterior 

 division of the posterior commissure. The fundamental divisions 

 appear less clearly defined than they do in Acanthias and, more- 

 over, they are not all evident at the same time as is the case in the 

 dog-fish. In Opsanus, the epiphyseal arch is present in the 

 smallest embryo studied as are also the posterior commissure 

 and intercalated part; all three can be seen during a brief period 

 (embryos of 3.5 to 5 mm.). By the time the posterior commissure 

 has grown over the pars intercalaris (embryo of 6.5 mm.), the velar 

 invagination is seen. The epiphyseal arch disappears with the 

 formation of the main epiphysis, the post-velar and paraphyseal 

 arches and the superior commissure presenting themselves at this 

 time (embryos of 8 mm.). 



As to the relation which these divisions bear to the neuromeres, 

 no direct evidence was obtained in the present study. Kupffer 

 ('06) has identified the region of Burckhardt's Zirbelpolster (Minot's 



