LIFE-CYCLE OF " CYSTOP.TA " TEKFGUTARTS (mINCH.). 89 



In this connection it is, I tliink, a significant fact tlmt, speak- 

 ing genea'allv; isogamy is most prevalent in the coclomic forms, 

 which are the most modified and which in certain instances 

 have developed neogaray. 



General Summaey. 



In conclusion, it may be said that Diplodina is a very 

 advanced and specialised Gregarine. Its principal modifica- 

 tions are those of non-motility, absence of cytoplasmic differ- 

 entiation, neogamy, and complete isogamy; these are closely 

 correlated with one another, and are for the most part ulti- 

 mately traceable to the degree of parasitism attained by the 

 genus. 



Diplodina and (also) Diplocystis are to be regarded as 

 forms which, following slightly different but parallel lines, 

 have pursued to the farthest extent Avhat may be described 

 as the main or typical course of evolution of a coelomic 

 Gregarine. 



University College, London, 

 July, 1905. 



Since the above was written only two or three papers 

 dealing with Gregarines have come under my observation. 

 There is only opportunity here to add a word or two with 

 reference to these, in so far as they bear upon the more 

 important points considered in my work. 



Reference has been made to Brasil's preliminary note on 

 the sexual reproduction of Monocystis. In 'Arch. Zool. 

 exp.' (4), vol. iv, p. 69, 1905, he describes the process in detail, 

 and it is apparent from his figures that the gametes resemble 

 those of Urospora and Gouospora. Besides the nuclear 

 differences between the two kinds of element, however, there 

 is also a slight inequality in size, one set (microgametes ?) 

 being rather smaller than the other (megagametes ?). 



Schnitzler ('Arch. Protistenk.', vol. vi, p. 309, 1905), in 

 describing the reproduction of Clepsydinia (Gregarina) 



