66 H. M. WOODCOCK. 



to bring forward any absolute proof that in Diplodina we 

 have to do with union at all, and not, on the contrary, with 

 division of varying incompleteness. It may be worth while, 

 therefore, to say briefly why the trophozoites of this genus 

 are to be regarded as couples, and not as individuals which 

 have undergone imperfect division. 



The case of Diplocystis schneideri is of much im- 

 portance in this connectiou. Here, also, is an instance where 

 neither a uninuclear individual nor the actual formation of a 

 pair has yet been observed. However, in D. major and 

 T). minor, two closely allied species, we have certainly to do 

 with the union of distinct individuals. Now, the condition 

 found in D. schneideri differs only very slightly from that 

 of the adult trophozoites of D. minor, and, as explained 

 above, is easily derivable therefrom. Hence it is hardly 

 open to doubt that D. schneideri is also an example of 

 precocious association, and not of early partial division. We 

 have seen, moreover, that in very young forms the septum 

 between the two halves may, apparently, be absent. 



The genus Diplocystis affords, perhaps, the strongest 

 argument in favour of a similar interpretation of the mor- 

 phology of Diplodina. One or two other corroborative 

 points may also be mentioned. Comparing trophozoites of 

 D. irregularis of different age, it is at once seen that, as 

 growth proceeds, the separation between the two halves of a 

 syzygy invariably becomes less instead of more pronounced. 

 It can confidently be said that the two members of a " couple " 

 never separate, which is the reverse of what one would expect 

 if they resulted from the division of a single individual. If 

 that were so, moreover, we should have conjugation taking 

 place between the progeny (gametes) of the two halves of 

 what was originally one individual (derived from one sporo- 

 zoite), an occurrence for which there is no precedent or 

 analogy among the Avhole of the Telosporidia. For these 

 reasons, therefore, I think it most likely that the trophozoites 

 of Diplodina — and equally, of course, those of Cyst obi a — 

 are correctly regarded as neogamous. 



