718 ]I. M. WOODCOCK. 



extended in a direction more or less transverse to the lonsr 

 axis of the body, this being doubtless brought about by the 

 separation of the daughter-ceutrosomes (cf. fig. 99); the 

 two centrosomes remain connected by a fibril, which at a 

 later stage may become considerabl}' drawn out (figs. 124, 

 125). The nuclear material becomes aggregated around these 

 two division centres ; as the latter continue to separate, it is 

 ])ulled out more or less into the form of a dumbbell and finally 

 constricted into two halves, the daughter trophonuclei. With 

 regard to the division of the kinetonucleus, the process, so far 

 as can be judged from the phases seen in figs. 101 and 104, 

 appears to be similar to that occurring in the division of the 

 other nucleus. A distinct thread or band connects the 

 separating halves ; this probabl}' indicates a fibril, corres- 

 ponding to the other, which may also have its terminations 

 in two intra-nuclear division-centres. If this is reallv the 

 case, not only the trophonucleus, but also the kinetonucleus, 

 possesses an intra-nuclear centrosome. 



(d) Comparison of Tr^-panosoma f ringillinarum 

 with other Avian species. 



The reasons which have led me to consider all the manifold 

 forms of the trypanosome met with as belonging to one and 

 the same species have been given at the commencement of 

 the description of the parasites, and also alluded to elsewhere 

 in the account, so that I need not recapitulate them here. 

 This illustration of the very great polymorphism which may 

 be shown by one species is most instructive. If, for instance, 

 only two t3'pes of form, at opposite extremes as regards size, 

 had been observed, it might readily have been supposed that 

 two different trypanosomes were concerned. And there can 

 be no doubt that many observers, not only of avian parasites 

 but also of others of cold-blooded vertebrates, who have based 

 their descriptions on casual observations of the parasites, 

 have fallen into such an error. So longf as the mammalian 

 forms, and among these chiefly the lethal ones, with their 

 comparatively modest variations in form and size, remained 



