No. I.] GAR-PIKE AND STURGEON. 51 



unlike that of Teleost, and is not strikingly different from that 

 of Elasmobranch, or even of urodele ; and in view of the un- 

 doubted kinship of Lepidosteus and Acipenser it seems impos- 

 sible to regard the peculiar growth of the latter as essentially 

 the more primitive and generalized. What the conditions have 

 been that have caused the flattened form-growth of the Stur- 

 geon is not easily to be established, but the greatly enlarged 

 outline of the embryo's head indicates the stages when they 

 are most prominently marked. The brain region in these 

 stages does not appear, accordingly, particularly suited for the 

 study of conditions which are to be regarded as undoubtedly 

 primitive: secondary characters, e.g., fusions of epiblast with 

 the roof of the fore-brain, or with the entoblast of the fore-gut, 

 appear to occur most confusingly. 



In concluding the above summary of the essential characters 

 of the early development of Lepidosteus and Acipenser an 

 especially noteworthy result should be emphasized — that Aci- 

 penser in its main development features seems the more 

 specialized type, but that it suggests in essential regards its 

 descent from a form not unlike Lepidosteus. The evidence thus 

 furnished seems to add the needed confirmation to the results 

 of Smith Woodward and Traquair, who have derived the Stur- 

 geons from a Palaeoniscoid stem, and recognized in this a close 

 kinship {e.g., through Dictyopyge and Catopterus) with the 

 scaly Ganoids. The Sturgeons (Smith Woodward) ' descending 

 from this stem have evolved an increased size and have degen- 

 erated or specialized in conditions of exoskeleton.' 



As to the evidence of the kinships of Ganoids afforded by 

 study of their early development : — 



Both A. Agassiz and Balfour and Parker have already em- 

 phasized the nearness developmentally of Gar-pike and Teleost, 

 Cf. Ref. 5, p. 430, (1H5). 



In addition to the teleostean characters previously noted the 

 present writer would add : — 



(i) Similarity in the mode of the first four cleavages. 



(2) Kindred relation of merocyte zone of germ disc to peri- 

 blast, suggesting that in the latter a thinning away of the 



