154 THE PROTOZOA 



of which gives rise to two sporozoites. In other cases (viz. Pfeiffcria 

 Labbe), a great number of nuclear divisions may take place, and the 

 final daughter-nuclei with their surrounding protoplasm form sporozo- 

 ites directly and without an intervening archispore stage. A similar 

 direct sporozoite-formation takes place among the Haemosporidiida, 

 the sporozoites being frequently of two kinds, macrosporozoites and 

 microsporozoites. While not established, it is probable that in all 

 forms this dimorphism in the spores has a sexual significance, the same 

 individual giving rise to only one form. One peculiarity of these 

 sporozoites is that the nucleus is apparently never provided with a 

 nuclear membrane, the chromatin, as in some flagellates, lying freely 

 in the plasm. 



Sporulation in the tribe Gymnosporea takes place without the pro- 

 tection of a cyst. The parasite rounds out, but does not secrete a 

 membrane. The nucleus divides into a great number of parts, which 

 migrate to the periphery as in other forms, and there divide. 

 Sporozoites are formed directly without preliminary spore-stages. 



An entirely different mode of sporulation occurs in the Myxospori- 

 diida, where the process is somewhat similar to the internal budding 

 of some of the Ciliata. In the genus Myxobolus, for example, one of 

 the numerous nuclei of the amoeboid form is surrounded by a thick- 

 ened mass of protoplasm, so that it can be distinguished from the 

 remainder of the animal. The thickened plasm soon forms a mantle 

 about the nucleus, which then divides by mitosis until there are ten or 

 a dozen daughter-nuclei within the specialized protoplasmic region 

 (Thelohan, '95 ; Gurley, '93). This mass, the sporoblast, which, how- 

 ever, does not quite correspond to the archispores of preceding types, 

 now divides into two equal parts, both of which remain inside of the 

 original protoplasmic mass. Each is an archispore, and each con- 

 tains three of the ten nuclei. The other four nuclei are left in the 

 free plasm within the membrane and soon degenerate and disap- 

 pear, corresponding, apparently, to the residual mass of chromatin 

 (polar body) of other forms. Each archispore next divides into three 

 cells (Biitschli, Balbiani for Myxobolus\ two of which are destined to 

 form peculiar thread-bearing capsules known as the polar capsules. 

 The other is much larger and represents the definitive spore. Each 

 sporoblast thus contains one spore, whose nucleus soon divides to 

 form the two nuclei which characterize the young myxospore. The 

 formation of the thread in the polar capsules according to Thelohan 

 ('95) seems to be the same in all species; a vacuole appears in each 

 of the smaller cells of the sporoblast (Fig. 86), then a small knob-like 

 projection grows up from one side of the vacuole, whose outer walls 

 harden until a distinct capsule is formed. The bud of protoplasm 

 within the vacuole now elongates and winds around until a spirally 



