LIFE-CYCLE OF " OYSTOBIA " IRREGULARIS (mINCH.). 65 



membraue to divide the two halves. For I have never seen 

 the least indication of absorption of the septum, during the 

 trophic phase, when it is present (see above, p, 25). Though 

 I have not had an ocular demonstration of the actual joining 

 so early, my fig. 32, showing in the wall of the respiratoi'y 

 tree a D. minchinii only 18 ju by 12 ju, not yet rounded off 

 since its entry, is strong evidence in support of this view. 

 The fact that I have never observed a uninuclear form, how- 

 ever small, in the wall of the tree, where the parasites are 

 readily distinguishable, also points to the same conclusion. 

 In addition, the universal occurrence of cytoplasmic fusion 

 in this species seems to imply that any unpaired individuals 

 very quickly die off, being probably quite unable to become 

 even young trophozoites alone. 



The union itself, in D. minchinii, most likely occurs in 

 the lumen before the parasites have penetrated into the wall. ^ 

 In D. irregularis, in those cases where the association is 

 between young trophozoites, it probably takes place in the 

 lumen of the blood-vessel; where neogamy is most intimate 

 it doubtless occurs when the individuals are little more than 

 sporozoites, but in what situation I am unable to say with 

 certainty. The passage of the parasites to their ultimate 

 situation may be very rapid, for I have often found intimately 

 associated trophozoites which have evagiuated the wall of the 

 vessel while very young (see above, p. 13). Probably in such 

 cases the sporozoites have associated at once, before passing 

 through the gut-wall and into the lumen of the vessel. 



The morphological condition found in Diplodina 

 is to be interpreted as one of union, and not of 

 imperfect division. — I am thus unable, it will be seen, 



1 Unfortunately, searciiing for very minute forms in this situation is most 

 difficult work, owing to the numbers of loose cells of various kinds, which 

 constitute in places a spongy tissue, tending to block up the lumen. More- 

 over, since the solitary sporozoites would not remain long in the lumen before 

 associating and passing into the tissue, only by very good fortune would one 

 come across them in a section. 



VOL. 50, TAKT 1. — NEW SERIES. 5 



