THE fl^MOFLAGELLATES. 201 



The female element is now a ripe megagamete or ovum 

 ready for fertilisation. The microgamete penetrates it at a 

 receptive cone, which arises from the cytoplasm on the side 

 where the female nuclei are situated. Its flagellar apparatus 

 disintegrates and disappears, and, in fact, the only parts 

 remaining distinct are the reduced male trophonucleus and 

 the still unreduced male kinetonucleus.^ The latter next 

 undergoes two reduction-divisions (not clearly made out), 

 and then the two trophonuclei unite to form the well-known 

 elongated " fusion-spindle," the kinetonuclei taking up a 

 position at either end of it, as in fig. 7. With this act 

 the zygote or copula arrives at the stage with which 

 this description began, and the complete cycle is now 

 accomplished. 



Section VI. Compakative Morphology of Trypanosombs. 



The body varies greatly with regard to size. Even in one 

 and the same species this is frequently noticeable, particu- 

 larly under different conditions of life ; and since, moreover, 

 different authors often give different estimates of the size of 

 a particular parasite, it is evident that any dimensions given 

 for purposes of comparison can only be considered as approxi- 

 mate. The common Trypanosoma rotatorium of frogs 

 (fig. 17 a and jb) is, taking it all in all, one of the largest 

 forms so far described. Its length ^ varies from 40 — 60 ju,'^ 

 while its greatest width dorso-veutrally * is from 8 — 30 fx ; 

 in the very wide examples breadth is gained more or less at 

 the expense of length. Conversely, T. gambiense, the 

 human parasite (fig. 16 c), is one of the smallest forms known. 



^ See footnote on previous page. 



' The length is always inclusive of the flagellum, unless otherwise stated. 



' The forms known as T. mega and T. karyozeukton, which are 

 closely allied, but probably distinct, species are somewhat longer. 



•• Adopting Leger's convention by which the convex side, bearing the 

 undulating membrane, is distinguished as dorsal ; the measurements of 

 width always include the undulating membrane. 



