30 Dr. F. Blochraann on the 



until the shells have separated, and then be again finally 

 expelled, or this expulsion may take place before the separa- 

 tion of the shells (fig. 9). During its sojourn in the plasma 

 of the intact animal the nucleus n^ changes its constitution. 

 At first it still distinctly shows the reticulated structure which 

 appeared in it at the time of the rupture of the plasma-thread 

 uniting it with the body of the animal. Gradually this struc- 

 ture disappears, and the nucleus acquires a more homogeneous 

 strongly shining appearance, while its outlines become irre- 

 gular (figs. 8 and 9). It therefore has exactly the aspect 

 which is presented by other nuclei which have perished. 

 Therefore it is like the nuclei undergoing degeneration during 

 the conjugation of Infusoria, or like the nuclei of Protozoa 

 which have been devoured by other Protozoa and partially 

 digested. As already stated, the nucleus is finally again 

 expelled. Then, however, the plasmatic envelope which it 

 originally possessed seems to be lost. It has therefore no 

 doubt been digested, while the nuclear substance itself appears 

 not to be assimilable. 



In this process therefore there results from a division which, 

 so far as one can judge, was normally commenced and carried 

 on, only a single individual, tlie plasma becoming retracted 

 again from the new-formed shell into the old one, while one 

 of the nuclei is thrown off. 



If we meet with a pair of animals, such as is represented in 

 fig. 1, and observe in it the processes described, of course it 

 seems a very probable notion that the two animals have 

 united by copulation. Now actual copulation and conjuga- 

 tion* do really occur, as I shall show further on. It is, 

 however, easy to distinguish a conjugation-pair from one pro- 

 duced by division. In the animals united by conjugation 

 there is very generally a mass of shell-lamellas in the plasma, 

 while this is not the case in the products of division, as it is 

 exactly the superfluous shell-plates of the parent animal that 

 are employed in the formation of the new shell. Further, in 

 stained preparations the young shell (II. in the figures) is 

 usually recognized with facility, because the individual plates 

 have separated from each other at different places. In conju- 

 gated animals I have always found, placed before the nucleus, 



* As will be sliown hereafter, both copulation (in which the plasma- 

 bodies of two animals become completely fused together to form a new 

 individual) and conjugation (in which the animals, after long-continued 

 union, separate again from each other, and in which hitherto no demon- 

 strable changes have been observed) do occur. For the sake of sim- 

 plicity 1 speak here always of conjugation-pairs, as they certainly con- 

 stitute the great majority of the united states which come under obser- 

 Tation. 



