of the Tripylean Radiolarin. 425 



but rather, from a certain point onwards, seem to constitute a 

 series of their own. 



At a particular stage the nucleus of Aulacantha sometimes 

 exhibits a pronounced cordate shape. The tip is directed 

 towards the oral pole, while the notch is situated opposite 

 to it on the aboral side. At the latter spot there arises an 

 invagination into the interior of the nucleus, which, though 

 at first small, continually increases in size. When the 

 internal cavitj has attained somewhat larger dimensions, on 

 rotating the central capsule through 90° on its main axis we 

 observe, besides other changes, before all things, a constriction 

 on the oral side of the nucleus. At a more advanced stage 

 the groove has increased in depth, while we notice that the 

 internal cavity is divided into two parts by a septum ex- 

 tending from the oral towards the aboral side. The septum 

 is not simple, but double, and the groove penetrates between 

 its two walls. 



There can be no doubt that it is in this plane that the 

 division of the nucleus is effected. Owing to the cavity in 

 their interior the daughter nuclei, on the separation of the 

 halves, possess a shape similar to that exhibited at a certain 

 stage in their development by the nuclei formed by division 

 of the equatorial plate. The finer structure, too, exhibits 

 many points of agreement, since in both cases the chromatin 

 is disposed in threads. 



Sometimes, and that not altogether seldom, stages in 

 nuclear division are observed that present an entirely different 

 appearance. In these cases apparently the object aimed at is 

 not attained. Since they do not admit of being ranged under 

 any precise method, I believe that their origin is to be 

 ascribed to a miscarriage of division. 



Karawaiew has already alluded to the fact that the division 

 of the central capsule of an individual is not under all circum- 

 stances immediately followed by a distribution of the rest of 

 the component parts of the body among the two daughter 

 individuals, but that through repeated division of the daughter 

 capsules the formation of a kind of colony may result. The 

 greatest number of the central capsules met with under such 

 circumstances amounted to five. I recently found a particu- 

 larly large specimen with as many as eight central capsules. 



It still remains for us to refer briefly to a few other stages. 

 In examining our material we now and again meet with 

 specimens in whose central capsule we fail to find the nucleus. 

 Instead, on the application of staining reagents for nuclei the 

 entire contents of the central capsule take a slight stain. A 

 closer study of prepared sections shows that in such cases the 



