274 THE SPOROZOA 



copulates with one of the numerous microgametes which penetrate 

 the female gamete (see p. 227). But in a large number of cases 

 Schaudinn observed that the reduced pronucleus underwent de- 

 generation, while the reduction-nuclei, on the contrary, flourished 

 and continued to divide, populating the macrogamete with a large 

 number of nuclei. In such cases, when the usual swarm of micro- 

 gametes entered the macrogamete, each microgamete copulated 

 with one of the numerous nuclei of the macrogamete, the result 

 being a process of multiple fertilisation of the macrogamete, round 

 which an oocyst is secreted in the usual way. There can be no 

 doubt that, as Schaudinn suggests, this multiple fertilisation is, 

 from the phylogenetic point of view, a reminiscence of an ancestral 

 condition in which the female gametocyte produced numerous 

 female gametes, each capable of being fertilised by a microgamete. 

 The effects of this multiple fertilisation upon the Cydospora are, 

 however, purely pathological, and lead to a complete degeneration 

 of the contents of the oocyst, which shrink and break up, with 

 production of a great quantity of brown pigment, in a way that 

 recalls the so-called " black spores " of the Haemosporidia (p. 253). 

 This is a striking instance of a pathological condition resulting 

 from a reversion to an ancestral mode of development. 



It follows from the homologies put forward above between 

 the gametes of Coccidia and those of Gregarines, that the cyst of 

 the latter is a formation functionally analogous, but not phylo- 

 genetically homologous, to the oocyst of the former. In both 

 types, however, the contents of the cyst are to be regarded as 

 equivalent, and the sporoblasts and spores (gymnospores or 

 chlamydospores) as strictly homologous in the two cases. The 

 first impulse towards the divergent evolution of the reproductive 

 phases of Gregarinida and Coccidiomorpha respectively probably 

 came from the acquisition, by the former, of an intercellular 

 trophic phase. There is, however, another group, the sub -order 

 Haemosporea, in which an intercellular trophic phase has been 

 acquired, and in which similar adaptations in the reproductive 

 phases might be expected to occur, but since next to nothing is 

 known at present with regard to the sexual reproduction of these 

 forms, it is impossible as yet to say how far such expectations are 

 fulfilled. 



SUB-CLASS NEOSPORIDIA. 



Sporor,oa in which reproduction goes on during the trophic phase. 

 ORDER 4. Myxosporidia. 



The Myxosporidia are one of the most populous and abundant 

 groups of the Sporozoa, exhibiting a wide range of structural 



