SUBKIKGLOM PROTOZOA. 



FlG - 



C ? IUS oliy acanthus 

 (after SCHNEIDER). 



a relatively large nucleus lying in tlie latter, and none are 



known to possess pseudopodia. Indeed in 



many Gregarinida a well-marked cuticle 



covers the exterior of the body (Fig. 11), 



sometimes distinctly striated or occasionally 



tuberculated. The Coccidia and many Gre- 



gariuida show little differentiation beyond 



what has been mentioned, but the Gregari- 



nida which inhabit Tracheate hosts usually 



present the appearance of being composed 



of two cells, owing to the anterior portion 



of the body being separated by a partition 



of ectoplasm from the posterior part, and in 



addition to this the anterior moiety in some 



cases is furnished with hooks, bristles, or 



finger-like processes (Fig. 11) of use in fixing 

 ,-, . T , , -i 11 \. , i , i-i 



the animal to the walls ol the cavity in which 



it lives. Even in these cases, however, but 



a single nucleus is present and the organism is unicellu- 



lar. 



Reproduction is carried on by spore-formation, preceded 

 in some cases by conjugation (Fig. 12), but simple division 

 or gemmation is not known to occur, apparent instances of 

 division being more probably cases of conjugation. In spore- 

 formation, preceded or not by conjugation, the animal as- 

 sumes a spherical shape and forms a cyst about itself, the 

 greater portion of the protoplasm splitting up into usually 

 a number of nucleated spores, a small portion of it, how- 

 ever, remaining undivided (residual body} (Fig. 12). When 

 mature the spores are usually spindle- or boat-shaped and 

 have received the name of pseudonavicetlce. They do not, 

 however, develop directly into Gregariues, but their proto- 

 plasmic contents break up into 2, 8, or more crescentic 

 spores (Fig. 12), a residual body being again formed as in 

 the formation of pseudonavicellae. The further history of 

 these crescentic spores is not thoroughly known, but in some 

 cases (Po/'ospora from the intestine of the lobster) each 

 seems to become converted into an amoaboid structure which 

 later elongates to an actively moving thread-like organism, 



