Protozoa. 23 



animals Protoplasta (first tissue). The amount of this 

 differentiation is in some scarcely recognisable, while in 

 others, the sun animalcules or Heliozoa (fig. 10), there are 

 many nuclei, and each of the fine ray-like pseudopodia 

 exhibits distinctly an inner axis of the granule-holding 

 protoplasm and an outer layer of firmer material. These 

 animals multiply by division, not the simple throwing off 

 of pseudopodia, but a division preceded by curious mole- 

 cular changes. In modes of feeding, &c., they resemble 

 the Rhi/opods, with which they are often united. 



Class 3, Gregarinae. A group of curious parasites, 

 the Gregarince, manifest a similar process of differentia- 

 tion taking place in their life-history. 

 These minute creatures are found in 

 the digestive canals of beetles, earth- 

 worms, &c., and in their mature states 

 they appear as elongated bodies with 

 a firm outer wall which never be- 

 comes protruded, and consequently 

 does not allow of the formation of 

 pseudopodia (fig. i, A, B). This 

 outer stratum may itself consist of A . Gregarine from the 

 two layers; while internally the *JHfc i * i * 

 protoplasm contains a solid nucleus. *-}^s*e from the 



dragon-fly. Ptxiuia 



At a certain stage in its existence focuia. 



P c. Boat-shaped body 



the adult Gregarine becomes almost or Pseudo-naviceiia. 



, . - . . , D. Amoebiform body 



globular and quiescent, loses its set free from Pseudo- 

 nucleus, and its internal material navicella - 

 becomes aggregated into many boat -shaped bodies, 

 contained within the firm outer layer through which 

 they eventually burst ; each of these boat-like bodies 

 (fig. uc) consists of a rigid outer case and an 1 inner 



