50 ARANEINA. 



aberrant ovary of Coccus. In this ovary the terminal chamber is filled 

 with cells which are united to a central rachis, as in Nematodes, and the 

 prolongation from the ovum is continuous with this rachis. This cord 

 is known as the yolk-duct (Dottergang) by German writers. Although it 

 is, not generally present in a distinct form, there is always a passage 

 connecting the ovum and yolk-cells, even when the follicular epithelium 

 grows in and nearly separates them. 



The number of nutritive cells varies from two (one ?) to 

 several dozen. After they have reached a maximum they gradu- 

 ally atrophy, and are finally absorbed without apparently fus- 

 ing directly with the ovum. The two types of insect ovaries 

 appear fundamentally to differ in this. In the one type all the 

 germinal cells develop into ova ; in the other the quantity is, so 

 to speak, sacrificed to the quality, and the majority of germinal 

 cells are modified so as to subserve the nutrition of the few. It 

 is still undecided whether the yolk-cells absolutely elaborate 

 yolk particles, or are merely conveyers of nutriment to the ovum. 



The egg-membranes of Insects present many points of in- 

 terest, which are however for the most part beyond the scope of 

 this work. There is always a chorion formed as a cuticular 

 deposit of the follicle cells, which is frequently sculptured, finely 

 perforated, etc., and is in many instances provided with a micro- 

 pyle, developed, according to Leydig, at the upper end of the 

 ovum. 



Its development at this point appears to be due to the fact 

 that the follicle is here incomplete ; so that the cuticular mem- 

 brane deposited by it is also incomplete. 



A true vitelline membrane can in many instances be demon- 

 strated (Donacia, etc.). 



ARANEINA. 



(65) Victor Carus. " Ueb. d. Entwick. d. Spinneneies. 1 ' Zcit.f. wiss. Zool., 

 Vol. ii. 1850. 



(56) v. Wittich. "Die Entstehung d. Arachnideneies im Eierstock, etc." 

 Mailer's Archiv. 1849. 



[Conf. Leydig, Balbiani, Ludwig (No. 4), etc.] 



The ova of many Araneina are remarkable for the presence 

 in the ovum of the so-called yolk-nucleus. The ova develop 

 from the epithelial cells lining the ovarian sack. Certain of these 

 cells grow large and project outwards, invested by the structure- 



