DESCEIPTION OP THE SEXUAL PRODUCTS. 



9 



saft), nuclear network, and nucleoli. The nuclear liquid is more 

 fluid than the yolk, in the fresh condition usually as clear as water, 

 and when coagulated by the addition of reagents, absorbs only 

 a little or no coloring matter. It is traversed by a network 

 of delicate filaments (hi), which attach themselves to the nuclear 

 membrane. In this network are enclosed nucleoli, or germinative 

 spots (kf), small, for the most part spherical, homogeneous, lustrous 

 structures, which consist of a Substance akin to protoplasm — nuclear 

 substance or nuclein. Nuclein is distinguishable from protoplasm — 

 in addition to certain other chemical reactions — especially by the 

 fact that it absorbs with great 

 avidity pigments such as car- 

 mioe, hsematoxylin, aniline, 

 etc., on account of which it has 

 also received from Flemming 

 the name chromatin. 



The number of the nucleoli 

 in the germinative vesicles of 

 different animals is highly 

 variable, but it is tolerably 

 constant for each species; 

 sometimes there is only a 

 single nucleolus present 

 (fig. 1), sometimes there are 

 several or even very many of 

 them (fig. 2,kf). Accordingly 



one may with Aueebach distinguish uninucleolar, plurinucleolar, 

 and multinucleolar germinative vesicles. 



At their surfaces eggs are surrounded by protective envelopes, the 

 number and condition of which are exceedingly variable throughout 

 the animal kingdom as well as among Vertebrates. It is best to 

 divide them, as Ludwig has done, according to their method of 

 origin, into two groups, into the prim,wry and the secondary egg- 

 membranes. Primary egg-membranes are such as have been pro- 

 duced either by the egg itself or by the follicular cells within the ovary 

 and the egg-foUicle, Those produced by the yolk of the egg are 

 called vitelline membrane ; those formed by the follicular epithelium, 

 chorion. All which take their origin outside of the ovary, as a 

 result of secretions on the part of the wall of the oviduct, are to be 

 designated as secondary egg-membranes. 



In their details the eggs of the various species of animals differ 



Fig, 2, — Germinative veaicle of a Frog's egg that 

 is still small and immature. It shows rery 

 numerous mostly peripheral germinative spots 

 (i/), in a fine nuclear network (An), m. Nu- 

 clear membrane. 



