SEX IN PROIOZOA 177 



the other w ith a smaller proloculiim, called microspheric. It was also 

 noted that microspheric individuals were commonly multinucleate 

 and that megalospheric ones were uninucleate. Many of the general 

 features of the life cycles including alternation of sexual with asexual 

 generations were worked out by such authors as Lister (1895), 

 Schaudinn (1903) and Winter (1907), but apparently Myers (1935, 

 1936) was the first to describe a complete life cycle with cytological 

 details. He found in FateUina corriigata and Spirillina vivipara (Fig. 

 O, a, 1 to 5): that all nuclei result from mitotic division of other 

 nuclei, instead of being formed from chromidia as postulated by 

 Schaudinn (1903); that gametes are amoeboid in these species (a, 4); 

 that gamete formation is preceded by the association of two or more 

 gamonts inside a cyst or temporary brood chamber (a, 3); that gam- 

 ete formation is accompanied by a reduction in chromosome number; 

 and that microspheric agamonts also surround themselves with a 

 temporary cyst before producing young megalospheric gamonts by 

 multiple fission (a, 2). Later Myers w^ent to England and was able 

 to corroborate the earlier accounts of life histories involving flagel- 

 lated gametes. 



As shown by Myers (1938), Die or bis patelUjonnis (Fig. O, b, 

 1 to 5 ) has a life cycle somewhat intermediate between that of Spiril- 

 lina vivipara (a) and Folystoinella crispa (c). The microspheric adult 

 (b, 1) gives rise to megalospheric offspring by a process of multiple 

 fission as shown by the other two species (b, 2). When these megalo- 

 spheric gamonts are mature, they associate in pairs with their ventral 

 surfaces in contact (b, 3). Between these parents a brood chamber is 

 formed in which flagellated gametes are produced (b, 4). These unite 

 in pairs, thus producing zygotes which develop into microspheric 

 young. These new individuals undergo growth and development to 

 a stage with several chambers before being released from the brood 

 chamber (b, 5). In Folystoiuella crispa there is no association of 

 gamonts before the formation of large numbers of flagellated gametes 

 (c, 4), so that fertilization is more a matter of chance than in the 

 other species illustrated. 



Foyn (1937) studied nuclear conditions in the microspheric 

 stages of Discorbijia vilardeboana. The adult shells had from seven- 

 teen to twenty-one chambers, and there was much variation in the 

 numbers of nuclei, their sizes, and their distribution among the 

 chambers. Schizogony was preceded by two mitotic divisions. In 



