EARLY CHANGES IN THE OVUM. lyj 



It is well known that in many of the Vermes the germs are 

 developed in one gland and the yelks in another, and that the 

 yelk and germ are only united during their passage through the 

 oviduct. 



I have shown elsewhere^ that there is the strongest evidence, 

 in my opinion, that in the fly the germs and yelks are developed 

 in separate follicles, and that the germ passes into the vitellus 

 immediately before the o^gg is impregnated and during its 

 passage through the oviduct. 



The evidence upon which this view rests depends upon the 

 developmental history of the ova and on the structure and con- 

 tents of the internal generative organs of the female insect. 

 The facts upon which I base my hypothesis that in the Fly, and 

 in Insects generally, the germ is developed separately from the 

 food-yelk and passes into it before the sperm, will be given 

 hereafter, and for the present I must refer my readers to my 

 published work on the subject already cited. 



I would only observe in this place that the ova of the Echino- 

 dermata are holoblastic, and that food-yelk is entirely, or almost 

 entirely, absent, so that the segmentation is absolutely regular 

 and equal ; that in the viviparous Peripatus, according to 

 Kennel,-f- the germ is without yelk, and undergoes equal segmen- 

 tation ; that in the viviparous Scorpions the germ is formed 

 before the yelk, and undergoes regular segmentation ; and in 

 the parthenogenic Aphides segmentation of the germ precedes 

 the formation of the yelk. 



If my contentions on this subject are correct, it follows that 

 segmentation, homologous with that of the Echinoderm, can 

 only affect the minute germ-yelk, whilst the food-yelk must be 

 regarded as a store of food material, which takes no part in the. 



* ' On the structure and development of the ovaries and their appendages 

 in the Blow-fly.' 'Journal of the Linnean Soc. Zool.,' vol. xx., 1889, pp. 418- 

 442. 



t Syncyiial Segmentation.— The phenomena described m Peripatus 

 as syncytial segmentation, appear to me to be due to imperfect fixation ; in 

 my earlier investigations I had numerous sections of Blow-fly embryos which 

 presented precisely the appearances figured by Sedgwick, which I subse- 

 quently learned to be delusive. (Compare Kennel [104].) 



