Miscellaneous. 231 



On the first Formation of the Body in the Vertebrata. 

 By Professor His. 



Professor His, in continuing his researches upon the ovular de- 

 velopment of the Vertebrata, has arrived at some results fitted to 

 produce a considerable change in the theory of blastodermic la- 

 mellae as modified by Remak. According to the author, the blas- 

 todermic lamellae would seem to constitute only secondary forma- 

 tions, and even the median lamella cannot at any period be regarded 

 as an anatomical whole. 



M. His distinguishes, from the first, in the hen's egg submitted 

 to incubation, two primitive blastodermic formations : at the ex- 

 pense of one are formed all the organs closely or distantly related 

 to the nervous system — the central nervous system, the peripheral 

 nerves, the epidermis, the glands, and the muscles, both striped and 

 smooth ; from the other originate the blood and the connective 

 tissues. The former is what is generally denominated the proli- 

 gerous disk ; but M. His gives it the name of archiblast or neuroblast ; 

 the latter is the white vitellus, or the parablast or heematoblast, ac- 

 cording to M. His. 



The archiblast is derived from what Meckel von Hemsbach de- 

 nominated the ovule properly so called — that is to say, the part of 

 the egg which undergoes segmentation after fecundation. The pa- 

 rablast, on the contrary, is an adventitious formation, comparable 

 to the cells of the granular tunic of the ovum in the Mammalia ; and 

 its constituent elements are similar in both the fecundated and un- 

 fecundated ovum. 



In the fecundated but not incubated egg, M. His distinguishes 

 the germinal disk and the white and yellow vitelli. The white 

 vitellus forms a thin stratum surrounding the yellow one, and is 

 prolonged beneath the germinal disk in the form of a cord to the 

 centre of the egg. The germinal disk is a thin plate which rests 

 upon the white vitellus, in the place where the ovule, properly so 

 called, occurs in the unfecundated egg. After fecundation, this 

 ovule, by segmentation, becomes converted into the germinal disk. 

 Beneath this there is a cavity filled with liquid, the bottom of which 

 is formed by the white vitellus. The peripheral part alone of the 

 germinal disk rests immediately upon the white vitellus. Their hue 

 of union is what M. His names the blastodermic circumvallation 

 (Keimwall). The part of the germinal disk beneath which the cavity 

 is situated is the pellucid area ; that which assists in forming the cir- 

 cumvallation is the opaque area. The author reverts to the opinion 

 of MM. Schwann and Reichert, according to which the elements of 

 the white vitellus are true nucleated cells. The cells of the germi- 

 nal disk form at first a continuous layer — the superior blastodermic 

 lamella. From the inner surface of this lamella start cords which 

 anastomose and form a sort of network, but never, before incuba- 

 tion, produce the true inferior blastodermic lamella. 



The first result of fecundation is the complete formation of the 



