g6 PROTOZOA 



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 " ^ 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 jfibrils 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 (I'-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 lirood-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." 



1 The cuticle in the allied genus Lanlcsteria, which is the form we figure on i>. 9;". 

 is perforated by a terminal pore, through which the clear plasma of the sarcocj'te 

 may protrude as a pseudopodiiim. 



- This account is taken from Cuenot (in Arcli. dc Biol. 1900, p. 49), which con- 

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

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

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

 preservation of his material. 



