24 INVERTEBRATE MORPHOLOGY. 



from the fact that the isospores are spherical in shape and 

 each possesses a peculiar whetstone-like crystal, wanting in 

 the macrospores. All the spores are provided with single 

 whip-like processes, flagella, by which they are propelled 

 through the water when set free from the parent. 



The various processes so far mentioned concern a single 

 individual only and are therefore non-sexual. Whether sex- 

 ual reproduction, the union of two individuals (conjugation}, 

 occurs among the Khizopods is uncertain, although the fusion 

 of two individuals preceding spore-formation has been ob- 

 served in several instances. That the fusion, however, is the 

 predisposing cause of the spore-formation seems probable, 

 but cannot be positively asserted until the behavior of the 

 nuclei of the two fused individuals is ascertained. It seems 

 exceedingly probable, also, that the macrospores and micro- 

 spores of the Eadiolaria are sexual cells, their further de- 

 velopment depending on the conjugation of a micro- with a 

 macrospore, but the fate of these spores has not as yet been 

 ascertained, and their conjugation can only be imagined from 

 analogy with other forms. 



II. CLASS SPOROZOA. 



The Sporozoa, which constitute the second class of Proto- 

 zoa, are all parasitic, living in the cavities, cells, or tissues of 

 other animals and deriving their nutrition from their hosts. 

 At present much is lacking to an adequate knowledge of the 

 various members of the group, but at least three orders are 

 to be recognized. 



1. Order Gregarinida. 



The Gregarinida include some of the largest Sporozoa, 

 and are parasitic either in the body-cavity, intestine, or 

 organs of various Invertebrata (especially in Annelids and 

 Tracheata), or in the cells especially of Vertebrated Animals, 

 these iutracellular parasites being .usually known as the 

 Coccidia in contradistinction to the former, the Gregariuida 

 proper. The members of both groups show a marked differ- 

 entiation of their protoplasm into ectoplasm and eudoplasm, 



