SEXUAL PHENOMENA IN THE PROTOZOA 



235 



while the failure to unite with the other nucleus leads to disintegra- 

 tion, and may be regarded as facultative reduction. 



The loss of nuclei through disintegration and absorption is better 

 established in the case of Actinosphcerium. Gruber ('83) and Brauer 

 ('94) maintained that the number of nuclei in old Actinosphceria is 

 reduced by fusion until only a few remain, but Hertwig ('98) shows 

 that with the exception of about 5 per cent, all of the nuclei atrophy 

 and are absorbed in the cytoplasm. The remaining nuclei, which he 

 calls the " sexual nuclei," then undergo so-called maturation divisions, 

 and fuse to form the cleavage nuclei of new cycles. 



A B 



Fig. 129. Conjugation of Euglypha alveolata Duj. [BLOCHMANN.] 

 n, functional nucleus, ri ', degenerating nucleus. 



D 





The simplest case of maturation comparable to that in Metazoa is 

 shown in two rather widely separated forms, Actinophrys, a heliozoon, 

 and Monocystis, a gregarine. In the former, Schaudinn ('96) observed 

 that, although the cytoplasms of two individuals fuse, the nuclei 

 remain apart. They finally divide by mitosis, and two of the daughter- 

 nuclei fuse, while the other two (polar bodies) disintegrate and are 

 absorbed in the cytoplasm (Fig. 130). Similarly in Monocystis, Wolters 

 {'91) has shown that two similar individuals join in a common cyst 

 and that the nuclei divide, one of the daughter-nuclei in each indi- 

 vidual disappearing in the plasm. 



In both of these cases, only one daughter-nucleus is eliminated in 

 each conjugant. In the other forms mentioned, there are at least two, 

 and the process approaches still more closely to maturation in Metazoa. 



