HELMINTHOLOGY IIELMINTHES NEMATODES. 457 



flattened ; the embryo itself does not increase in length at 

 both extremities, but always appears convoluted, so that 

 Kolliker supposes that the mass of embryonic cells is trans- 

 formed at once into a spirally convoluted embryo. The young 

 flattened worm consists of a soft, transversely wrinkled, 

 external integument, and of a granular substance contained 

 within it ; it presents neither mouth, anus, nor generative 

 opening. The granular substance is regarded by Kolliker 

 as the first indication of the intestinal canal, with the com- 

 mencement of the oesophagus and stomach already marked 

 out. He also observed complete fission of the yolk in the 

 CucuUanus of the Slow-worm. (Entwicklungsgeschichte 

 der Cephalopoden, p. 121.) 



In Ascaris dentata, Kolliker (Miiller's Archiv, 1843, 

 p. 69) observed the external orifice of the female organs, as 

 a transverse fissure almost in the middle of the body. The 

 internal generative organs, as in other female Round-Avorms, 

 are divided into two portions, one of which fills the anterior 

 and the other the posterior part of the body. The ova of 

 this Ascaris dentata attain, Avithiii the body of the mother, 

 a very considerable degree of development. The more par- 

 ticular examination and observation of the extremities of the 

 ovarian tubes led Kolliker to conclude that those tubes are, 

 at the point, constituted of a single row of cells, the walls of 

 which, where they are in mutual apposition, disappear in 

 course of time, and that their cavities, thus communicating, 

 constitute the canal of the ovary. By a repetition of this 

 process the ovarian tube increases in size and length. At the 

 extremity of these ovarian tubes Kolliker observed the forma- 

 tion of the ovum, in the progress of which he perceived that 

 the germinal spot is the first formed structure in' the ovum, 

 around which the germinal vesicle is formed like a primitive cell 

 around the nucleus, and around which subsequently granules 

 are deposited, constituting the vitellus and a secondary cell, 

 the vitelline membrane. Kolliker confirms Bagge's and 

 the Reporter's observation made on Strot/yylus auricularis 

 and Ascaris acuminata, that all the ova which have traversed 



