of a Species of Chiron onrns. 43 



vitellus increases, it collects in the lower extremity of the 

 ovum ; and the luicleus, which is already the germinal vesicle, 

 descending tn^n the upper extremity, bm-ics itself in the con- 

 stantly incrcfising vitelline mass. The chorion, however, is 

 formed by the activity of the epithelial layer of the tunica 

 propria] but whether this structure is formed as a cuticular 

 deposit of the epithelial cells, as described by Leydig*, or the 

 epithelial cells are directly converted into the chorion, as stated 

 by Stcinf, I am unable to say]:. 



It is therefore clear that the germinal vesicle of the ovum 

 has originated from the nucleus, and the vitellus with the oil- 

 drops and the chorion (corresponding to the epithelial cells of 

 the tunica propria) from the vitelligenous cells, which repi-e- 

 sent the embryonal cells of the ovarian tube. But when we 

 remember that the ovarian tube has been produced by the 

 conversion of the ])olar cell, that the nucleus of the former 

 («', e. the ovarian tube) is only a portion of the nucleus of the 

 latter (t. e. the polar cell), and the nucleus of the polar cell, 

 again, is only a part of the germinal vesicle, we become con- 

 vinced that this generation stands in direct connexion with 

 the preceding one, and that its germinal vesicle is only a part 

 of that of the lirst§. 



W, Keferstein in 'Zeitschr. fiir rat. Medicin,' 1862, Bd. xiii. pp. 198, 199). 

 The same opinion is also partially supported by Claus, who says that 

 '• epithelial cells, vitelligenous cells, and ova " («'. e. the germinal vesicles ; 

 but we have already seen that these are of diflerent origin from the 

 vitelligenous cells, and therefore we cannot agi-ee with him) " are modi- 

 fications of originally homogeneous elements, that they have proceeded 

 genetically from the same cells, and by a ditierent mode of development 

 nave attained such divergence of fonu " (/. c. p. 44). Stein thinks that 

 the epithelial cells also take part in the formation of the vitellus ; and 

 Leydig is of opinion that they only secrete the chorion (Der Eierstock 

 &c. p. o7) ; but nevertheless he admits their affinity to the ova in other 

 animals, resting his opinion upon the investigation of La Vallette (ibid. 

 p. 50, note 1). "With regard to Metschnikow's opinion, vide supra. 



* Leydig very accurately describes the development of all the layers 

 of the chorion in Timarcha tcnehricosa (see his ' Eierstock und Saraen- 

 tasche,' pp. 11, 14, and o7, Taf. 2. tigs. 7-10). t Leydig, /. c. p. o9. 



X Meyer ("Ueber die Entwickluu^ des Fettkorpers, &c.," Zeitschr. fiii- 

 wiss. Zool. Bd. i. p. 19-3) says that when the vitellus collects, the epithe- 

 lial cells divide in the dii-ection of the radii of the ovum, and lie with 

 their outer ends on the chorion, and " strengthen it," and afterwards, 

 " whilst the epithelial cells amalgamate with the chorion, they become 

 thick- walled, unite firmly with each other, and lose their nuclei." 



§ M. Ganin (" Beitriige zur Erkenntniss der Entwicklungsgeschichte der 

 Insecten," Zeitschr. fur wiss. Zool. 1869, p. .387) says : — " At any rate, it is 

 clear that both the central cell and its nucleus (from which the embryo 

 is developed) must be regarded as new fonnations." It seems to me, 

 however, that this opinion is by no means correct, any more than Weis- 

 mann's theory of the free formation of the germ-cells, which has recently 

 been supported by Ganin in the Pteromalinse {ibid, p. 439). 



