8UBKIJSODOM PROTOZOA. 



25 



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

 known to possess pseudopodia. Indeed in 

 many Gregarinida a well-marked cuticle 

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

 sometimes distinctly striated or occasionally 

 tuberculated. The Coccidia and many Gre- 

 garinida 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 ^^«- ^^--Hoplorhyn- 

 ,, . 1 , ,1 n p ,1 ■, ■ 1 • T c/ws oligacanthus 



the animal to the walls of the cavity m which (^.fter Schneider). 



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 hody) (Fig. 12). When 

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

 have received the name of pseudonavicdlce. They do not, 

 however, develop directly into Gregarines, 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 pseudonavicellse. The further history of 

 these crescentic spores is not thoroughly known, but in some 

 cases (Porospora from the intestine of the lobster) each 

 seems to become converted into an amoeboid structure which 

 later elongates to an actively moving thread-like organism, 



