324 BIOLOGY OF THE PROTOZOA 



described by Schroder (1907) for Sphaeromyxa sabrazesi, a parasite 

 of the sea horse, where the multinucleate ameboid body of the 

 parasite contains two kinds of nuclei distinguishable by size and 

 structure. Within the protoplasmic body small areas become differ- 

 entiated from the surrounding cytoplasm. These areas, character- 

 istic of the Myxosporidia, each contain 2 nuclei, 1 of each kind 

 (Fig. 164, K-Q). With the development of the pansporoblast, 

 each nucleus divides in such order that 7 daughter nuclei finally 

 result from each, the 14 nuclei behaving as follows: 2 are destined 

 to degenerate as "reduction nuclei;" 4 become the centers of capsule 

 and shell formation; 4 become centers of polar capsule formation; 

 and 4 remain as germinal nuclei. The protoplasm of the pansporo- 

 blast divides into two halves (M), the sporoblasts, and each contains 

 6 of the nuclei, while the 2 degenerating nuclei remain outside. 

 The 6 nuclei are thus differentiated into somatic and germinal 

 nuclei 4 in each case going into somatic differentiations of the spores 

 (shells, polar capsules and threads) and 2, presumably 1 of each of 

 the original two kinds, remain as pronuclei (N, 0, P). 



Many different observers have noted this binucleated stage of the 

 young spore, and the problem of fertilization in Myxosporidia 

 appears to be bound up with their further fate. Schroder believes 

 that they unite later and so complete the fertilization, a belief 

 which he was able to prove in a later publication (1910). Keys- 

 selitz (1908), working on Myxobolus pfeifferi, likewise believed in 

 the union of an analogous pair of nuclei during either the final 

 stage of development of the spore or in the young animal immediately 

 after leaving the spore case (Fig. 164, A-T). Davis (1916) observed 

 the union of such nuclei in Sphaerophora dimorpha but was some- 

 what skeptical of his own observations, but Erdmann (1911 and 

 1917) confirmed Schroder in actually observing the fusion. Awer- 

 inzew (1909) on the other hand, working with Cer atomy xa drepano- 

 psettae, believed that fusion or fertilization does not occur in the 

 spore stage but after the initial development of the young animal 

 (see also Kudo, 1924). When the latter has reached the stage with 

 4 nuclei, 2 of the nuclei become trophic while the other 2 become 

 germinal giving rise by division to "microgametes" and macro- 

 gametes which fuse after "reduction." Mavor (1916) working with 

 an allied species {Cer atomy xa acadiensis) found uninucleate young 

 forms which, upon the first division of the nucleus, give rise to 

 dimorphic nuclei as described by Awerinzew. The fusion of "gam- 

 etes" which Awerinzew T described was confirmed in part by Keys- 

 selitz (1908) in connection with Myxobolus pfeifferi. Here the 

 pansporoblasts which Keysselitz names the "propagation" cells, 

 arise in the protoplasm of the adult organisms in the same manner 

 as in other Myxosporidia, but the nuclei, and w r ith them the cell 

 body of the germinal area, divide (Fig. 164, A, B, C). The prop- 



