Quain's elements of anatomy . e observation of invagination inthe lower vertebrates. (See No. 75.) The existence of a neurenteric canal or blastopore in birds was discovered byGasser in 1879 (No. 103), and has been confiimed by Balfour and Braun; andfrom these observations it appears that it is subject to some variation in positionand extent in that class of animals. 762 RELATION OF BLASTODERM TO DEVELOPMENT. This discovery was extended to the class of Reptiles (Lizards) by Ktipffer andBenecko in 1879 (No. 112), and confirmed by original observations by Balfour ; anda foitlier series of resear
Quain's elements of anatomy . e observation of invagination inthe lower vertebrates. (See No. 75.) The existence of a neurenteric canal or blastopore in birds was discovered byGasser in 1879 (No. 103), and has been confiimed by Balfour and Braun; andfrom these observations it appears that it is subject to some variation in positionand extent in that class of animals. 762 RELATION OF BLASTODERM TO DEVELOPMENT. This discovery was extended to the class of Reptiles (Lizards) by Ktipffer andBenecko in 1879 (No. 112), and confirmed by original observations by Balfour ; anda foitlier series of researches by Kupffer (No. ll.^) in the present year, have shown,that the nenrenteric canal exists in Ophidia and Chelonia. We owe to Hensen the fiist clear account of the development of the primitivestreak in mammals (rabbit), and his observations have been ably followedTip by Kolliker. The observations of Schafer on the early blastoderm of theguinea-pig have shown more clearly the connection subsisting between the lower Fig. Fig. 656,—Diagrammatic Longitudinal Section of an Embryo of Lacerta. (From Balfour.)2}p, body cavity; am, amnion fold ; nc, neui-enteric canal; cli, notochord ; hy, hypo-blast; ep, epiblast of the medullary plate ; pr, primitive streak. In the primitivestreak aJl the layers are partially fused. layer in the medullary or embryonic region and the epiblast and mesoblast in theanterior extiemity of the primitive sti-eak, and according to Balfour a comparisonof this with the conditions observed in reptiles and birds leaves little doubt thatthis union may be looked upon as the dorsal lip of a blastopore. In the mole (andpartially also in the rabbit) Heape has ascertained the existence of a neurenteriocanal similar to that observed in other vertebrates (No. 107). This appears firstas a pit at the anterior extremity of the primitive streak, and in later stages per-forates the floor of the hinder end of the medullary groove. A. Fraser also hasseen the neui-enter
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