68 H. M. WOODCOCK. 



rent iutimacj' of tlie two members of the couple ia those 

 cases where the septum is absent, it may safely be said that 

 there is nothing approaching a true conjugation as yet 

 between the two halves. Though I have many a time found 

 the two nuclei in contact, T do not believe there is any 

 nuclear fusion or interchange of material ; for I have uever 

 seen the slightest sign of a break-dowu in the nuclear wall 

 or of alteration in the nuclear constituents. 



It is more difficult to be certain with regard to the cyto- 

 plasm. Personally, I think the two cytoplasms remain (until 

 sporulation) as individually distinct in the cases where there 

 is no septum as in those where it is present. The fact that 

 in D. irregularis the septum may persist until nuclear 

 multiplication is considerably advanced, when the two cell 

 territories remain for the time being quite separate, renders 

 it highly probable that this is true when the septum is 

 absent, although the delimiting plane is not distinguishable. 

 The reason for the inability to see the plane of junction in 

 such a case is not, I consider, because it is no longer there, 

 but because it is not constituted by a layer (ectoplasm, or 

 limiting membrane) different from the general cytoplasm. 



In all the other Gregarines whose life-history has been 

 investigated the complete morphological '^ separateness" of 

 the cytoplasm of the two associates is a recognised feature 

 (see Introduction, p. 5), and there is no reason to suppose it 

 is otherwise in Diplodina. That there is any complete and 

 homogeneous intermingling of the cytoplasm of the two indi- 

 viduals, resulting in one binuclear organism, I do not for a 

 moment believe ; such an actual merging of two distinct 

 entities into one takes place first later, when the gametes 

 copulate. Association certainly gives a stimulus to further 

 development, and, as Ave have seen, neither growth nor life 

 can go on in Diplodina without neogamy. Nevertheless, I 

 think that such stimulus is principally cytotactic (see below, 

 p. 73), and of a radically diffcre'nt character from that which 

 is imparted by true conjugation.^ 



' Sec Heiiwig's suggestive essay (14) on tlic siguiliciiuce of fcrtiHsaliou. 



