40 ARANEINA. 



passing down the tube becomes gradually invested by a layer of 

 epithelial cells, which in many cases pass in and partially separate 

 the ovum from the nutritive cells. The epithelium appears not 

 unfrequently to be continued as a flat layer between the nutritive 

 cells and the wall of the egg-tube, 



As was first shewn by Huxley and Lubbock, the protoplasm of the 

 ovum is often continued up as a solid cord, which terminates freely between 

 the nutritive cells, and serves to bring to the ovum the material elaborated 

 by them. It is present in its most primitive form in the somewhat 

 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 gradually atrophy, 

 and are finally absorbed without apparently fusing 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 nutri- 

 ment to the ovum. 



The egg-membranes of Insects present many points of interest, 

 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 micropyle, 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 membrane 

 deposited by it is also incomplete. 



A true vitelline membrane can in many instances be demonstrated 

 (Donacia, etc.). 



ARANEINA. 



(55) Victor Carus. "Ueb. d. Entwick. d. Spinneneies." Zeit. f. wiss. Zoul., 

 Vol. ii. 1850. 



(56) v. Wittich. "DieEntstehuug d. Arachnideneies im Eierstock, etc." Mullens 

 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 develope from the 

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

 large and project outwards, invested by the structureless membrane of 

 the ovarian wall. The stalks of projections so formed are turned to- 



