of a Species of Chironomus. 107 



the investigations of Leuckart*, Ganinf, and MetschnikowJ, 

 as they have detected the ovaries in the Cecidomyid larvce, 

 and studied the genesis of the larvae from the ova. Indeed 

 Prof. Wagner himself afterwards recognized his error. 



When a certain number of ova have attained maturity 

 within the organism of the parent pupa, the pupa expels them, 

 through the above-mentioned orifices situated in the penul- 

 timate ventral segment, in the form of two cords consisting of 

 a homogeneous mass, in each of which there are from 20 to 50 

 ova. These newly laid ova are elongated oval, egg-shaped, 

 with an obtuse and an acute pole. In the former the 

 head of the embryo is afterwards situated ; and it is there- 

 fore indicated as the cephalic pole, whilst the opposite one is 

 named the caudal pole. The ova are 0*22 millim. in length 

 and 0*09 millim. in breadth. They are filled with a brownish- 

 yellow vitellus, which contains a quantity of rather large oil- 

 drops. At the upper or cephalic pole the chorion forms an 

 impression, on the margins of which is affixed an extremely 

 elegant lobule (PI. III. fig. 12, I) which formerly united the 

 ova with one another. Whether there is a microj)ylar orifice 

 in this impression I do not know. 



In the preceding chapter we have seen that in the ovum 

 when still incompletely developed but already half filled with 

 tlie yelk, and changed from the conical to the oval form, the 

 germinal vesicle was already present, although the germinal 

 spot could not be found in it. From this circumstance alone 

 we might come to the conclusion that the germinal vesicle 

 exists in the perfectly developed and deposited ovum ; never- 

 theless all my endeavours to discover the germinal vesicle 

 were without result, although I resorted to the most various 

 reagents and methods of investigation. Notwithstanding this, 

 however, I was firmly convinced that the so-called germ- 

 nuclei are developed in the ovum of Chironom^is^ as indeed of 

 all insects, by the division of the germinal vesicle. We know 

 that the germinal vesicles have originated by the division of 

 the nucleus of the ovarian tube. This circumstance alone 

 leads us to assume that the germinal vesicle also divides and 

 thus produces the germ -nuclei, but not that it is destroyed ; for 

 in agamic reproduction the fecundation which ought to cause 

 this destruction of the germinal vesicle is wanting. And in 

 fact, after I had in vain examined many hundred ova with this 



* " Die imgeschlechtliclie Fortpflanzung der Cecidomyienlarven," Arch, 

 fiir Naturg. 1865, p. 290. 



t Zapiski Imp. Ak. Nauk, 1865, vol. vii. p. 46. 



X Zhurnal Mni. Nar. Pr. 1865 : Embryologische Studien an Insecten, 

 p. 20. 



8* 



