g6 PROTOZOA 



CHAP. 



muscles of Metazoa ; besides these it contains proteid granules 

 which stain with carmine, and oil-drops. The ectosarc is formed 

 of three layers : (1) the outer layer or " cuticle " 1 is, in many cases 

 if not here, ribbed, with minute pores in the furrows, and is 

 always porous enough to allow the diffusion of dissolved nutriment ; 

 (2) a clear plasmatic layer, the " sarcocyte " ; (3) the "myocyte," 

 formed of " myonemes," muscular fibrils disposed in a network 

 with transverse meshes, which effect the wriggling movements of 

 the cell. The endosarc contains the granules and the large 

 central nucleus. The adult becomes free in the seminal vesicles ; 

 here two approximate, and surround themselves with a common 

 cyst : a process which has received the name of " association " 

 (Fig. 31, g-i). Within this, however, the protoplasms remain 

 absolutely distinct. The nucleus undergoes peculiar changes by 

 which its volume is considerably reduced. When this process of 

 " nuclear reduction " is completed, each of the mates undergoes 

 brood-divisions (J), so as to give rise to a large number of 

 rounded naked 1 -nucleate cells the true pairing-cells. These 

 unite two and two, and so form the 1 -nucleate spores (k-m), 

 which become oat-shaped, form a dense cyst-wall, and have been 

 termed " pseudonavicellae " from their likeness to the Diatoma- 

 ceous genus Navicella. Some of the cytoplasm of the original 

 cells remains over unused, as " epiplasm," and ultimately degene- 

 rates, as do a certain number of the brood-cells which presum- 

 ably have failed to pair. It is believed that the brood -cells 

 from the same parent will not unite together. The contents 

 of each spore have again undergone brood-division to form eight 

 sickle-shaped zoospores, or " sporozoites " (n-q), and thus the 

 developmental cycle is completed. Probably the spores, swallowed 

 by birds, pass out in their excrement, and when eaten by an 

 earthworm open in its gut ; the freed sickle -germs can now 

 migrate through the tissues to the seminal funnels, in the cells of 

 which they grow, ultimately becoming free in the seminal vesicles. 2 



1 The cuticle in the allied genus Lankesteria, which is the form we figure on p. 95, 

 is perforated by a terminal pore, through which the clear plasma of the sarcocyte 

 may protrude as a pseudopodium. 



2 This account is taken from Cuenot (in Arch, de Biol. 1900, p. 49), which con- 

 firms Siedlecki's account of the process in the allied genus Lankesteria in Bull. 

 Acad. Cracow, 1899. Wolters's previous description, assimilating the processes 

 to those of Actinophrys, is by these authors explained as the result of imperfect 

 preservation of his material. 



