170 EDOUAKD VAN BENEDEN. 



microchemical characters of tlie element and of its various 

 parts — to wit, the nuclear membrane, the body of the nucleus, 

 and the nucleoli. It depends eiitirely on the phenomena which 

 one knows in relation to the vital manifestations, the de- 

 velopment and the multiplication of nuclei. 



If one breaks the tnembrane of the egg of a Starfish so as 

 to allow the contents of the egg to escape into weak osmic 

 acid or picric acid, the germinal vesicle presents a peculiarity 

 which I have been able also to make out in the living eggy 

 after having first observed it in the germinal vesicle isolated 

 and treated with these reagents. In the nucleus of the egg 

 there exists a network with large meshes, formed by a very 

 finely granular substance. It is in this reticulum that the 

 pseudo-nucleoli are found ; the germinal spot appears to be 

 the centre from which the reticulated filaments start. The 

 characters of this network vary, moreover, in difierent ova ; 

 sometimes one even sees in place of the network a small 

 granular collection formed by the substance of the reticulum 

 and the pseudo-nucleoli. This reticulum I have also found 

 in the rabbit, and I have proposed to designate the substance 

 which constitutes it by the name of nucleo-plasma. The 

 first to describe a network similar to that of the Starfish was 

 W. Flemming.^ He found that in the Anodons and the 

 Unios the transparent liquid of the germinal vesicle is 

 traversed by numerous anastomosing filaments. Kleinenberg 

 has mentioned something similar in the germinal vesicle of 

 the fresh- water Hydra ; and lastly Hertwig has observed it in 

 the Toxopneustes lividus and in the ova of the mouse. I do 

 not know that anything of a similar nature has been shown to 

 exist in other nuclei of cells. I think, therefore, it will not 

 be without interest to mention here my observations on the 

 constitution of the nucleus of an enormous cell which con- 

 stitutes by itself alone the whole central part of the body 

 (Leibeshohle of Kolliker) of the Dicyema. The nucleus, 

 which is more or less regularly ellipsoid in shape, presents a 

 thick membrane, beneath which there exists a very close 

 network composed of a finely granular material, whilst the 

 contents of the nucleus [nuclear substance) are perfectly 

 homogeneous and transparent. The body of the nucleus is 

 traversed in certain individuals by a reticulum which makes 

 it resemble a spongy tissue; in other individuals there exists 

 only a bundle of filaments like pseudopodia. I have re- 

 presented one of these nuclei (figs. £0 and 21). By the 

 application of the picrocarminate after previous treat- 



' W. riemming : " Studien in der Entwickelungsgeschichte der Naja- 

 den," ' Sitzb. der K. Acad, der Wissenscb. zu. WieD.,' vol. Ixxi. 



