88 THE INVERTEBRATA 



products of the first of two successive multiple fissions whereby the 

 sporozoites and other spore-like stages often arise. In the Neosporidia 

 it denotes the syncytia (of different origins in different groups) from 

 which by differentiation of cells complex spores are formed. 



Subclass TELOSPORIDIA 



Sporozoa in which the adult of the vegetative stage has only one 

 nucleus; and comes to an end with spore formation; and the spore 

 cases, if present, are simple structures, which nearly always contain 

 several sporozoites. 



The vegetative stage {trophozoite) has usually a definite shape, but 

 in some haemosporidia is amoeboid. Its fission (agamogony), if such 

 occur, is multiple, and is usually known as schizogony^ the term schizo- 

 zoites or merozoites being applied to the offspring. Its single nucleus 

 only divides to form those of the young into which this stage breaks up, 

 but owing to such division the body may be for a while multinucleate. 

 The trophozoite of one of the two orders (the Coccidiomorpha) 

 remains intracellular: in the other order (the Gregarinidea) it after 

 a time outgrows its cell host. Save in one suborder (Eugregarinaria), 

 it passes through the usual phase of agamogony before giving rise to 

 gamonts, but in the Eugregarinaria agamogony is omitted, and the 

 members of the single vegetative generation become gamonts, which 

 provide for the increase of the species by the formation of many 

 gametes in both sexes. The gamonts may be free or intracellular. 

 Free individuals are often able to adhere by a sticky secretion, form- 

 ing what is known as a syzygy. When gamonts so adhere (Figs. 76, 

 6; 77 B) they do so in pairs^ whose members are to be the parents of 

 gametes that will unite reciprocally. Syngamy is isogamous in a few 

 of the Gregarinidea, but is usually anisogamous, and in the Cocci- 

 diomorpha becomes an oogamy (p. 31). In some cases, perhaps in 

 all, the first division of the zygote is a reduction division, so that 

 nearly the whole of the cycle is haploid. 



The little group Piroplasmidea, whose members in some respects 

 resemble the Telosporidia, are best placed as an appendix to this 

 subclass. 



Order COCCIDIOMORPHA 



Telosporidia in which the adult trophozoite remains intracellular; 

 and the female gamete is a hologamete. 



Typically the members of this order are parasites of the gut, but 

 more than once they have come to infest the blood. One such invasion 

 gave rise to the suborder Haemosporidia. The rest of the group con- 

 stitute the Coccidia. 



^ The term syzygy should perhaps be restricted to such pairs. 



