78 H. M. WOODCOCK. 



of very intimate association^ in this species, renders it not 

 unlikel}^ that such an encysted couple, wlien sporulating, may 

 have been mistaken for a single individual. Again, a species 

 of Selenidium from the gut of Spio martinensis appears 

 to encyst as often singly as in couples, nuclear changes taking 

 place in both cases (see C.and M. [5]). Actual spore-forma- 

 tion, however, was never observed, since sporulatiou is 

 not completed while the parasites remain inside the host. 

 S. echinatum, from Dodeceria, exhibits the same latitude 

 in the matter of encystment. Nevertheless, C. and M. state 

 (6) that in three hosts in which spore-containing cysts were 

 found they were undoubtedly normal, constituted in all cases 

 by associated couples. 



To sum up, we may say that while, except in Ophryo- 

 cystis, successful independent sporuiation cannot be re- 

 garded as proved, it is not improbable that such a modifica- 

 tion of the typical life-history may be met with, in special 

 circumstances. Consider Gonospora varia, for example. 

 Here we have a coelomic parasite which is non-motile, but 

 which has not developed neogamy. Hence association, just 

 when desired, must be more or less precarious. It would not 

 be surprising, therefore, to find that this form had acquired 

 the ability to develop also parthenogenetically. There can be, 

 however, little doubt, I think, when the whole line of argument 

 of this and the preceding section is considered, that if such 

 independent sporulatiou occurs, it is only after prior tem- 

 porary association.^ Such association, although the tropho- 



1 In certain cases, Caullery and Mesnil observed that the partition dividing 

 the two associates disappeared. Brasil (loc. cit.) pointsout llie analogy between 

 this occurrence and the neogamy of Cystobia [Diplodina]. It probably also 

 represents a step taken to bring about permanent association ; it will be seen, 

 however, that tliis parasite is proceeding upon a slightly different line from that 

 taken by Diplodina, where the septum, once formed, never breaks down (in 

 trophic life). 



2 Commenting upon association in the Selenidium from Spio, Caullery 

 and Mesnil (loc. cit.) say that the adherence of the two members is very 

 feeble, and tiiey are easily and often separated. Hence, it is extremely probable 

 that the individuals which sporulate alone have at one time or another been 

 associated. 



