THE HJ!MOFLAGELLATES. 227 



Lastly, it must be remembered that, even if, in some of the binary unions, 

 the kinetonuclei themselves join, as Bradford and Plimmer have supposed, 

 these are not to be regarded as sexual nuclei, comparable to micronuclei (see 

 above, p. 200, footnote). 



Bearing in mind, however, the recent work of Calkins and others 

 upon the essential meaning of fertilisation, a remark of Lignieres (71) 

 is not without interest in this connection. This author investigated the 

 phenomenon in T. equinum, where binary unions are very frequent but 

 fugitive, separation (disagglomeration) readily occurring. He considers it 

 quite probable that, as a result of the close intimacy, a molecular inter- 

 change goes on between the associates. The process may be stimulating or 

 recuperative, induced by the effect of the changes in tlie environment. It 

 is, moreover, somewhat suggestive that the agglomeration is, generally, at 

 first binary, and sometimes (though not often) tends to remains so. Can 

 the process perhaps be considered as affording hints of aplastogamicunion? 

 It is evident that much has still to be learnt respecting the biological 

 meaning of agglomeration. 



(c) Abnormal and Involution Forms. 



Involution and degenerative stages of Trypanosomes have received atten- 

 tion, and acquired an importance altogether undeserved, owing, chiefly, to 

 the fact that many of the pai-asites have been studied, so far, only in strange 

 and unaccustomed hosts, hosts to which they are unadapted, and for which 

 they, on their part, prove markedly pathogenic. Tliat these forms are the 

 outcome of the unusual environment seems clearly proved by the fact that 

 the}' are rarely or never described in tlie case of the many tolerated para- 

 sites now known. For being the first to suggest the real significance of 

 the weird shapes often met with, and thus throwing light upon much that 

 had greatly puzzled previous investigators, students of the group are 

 indebted to Laveran and Mesnil, and this is, from the point of view of 

 zoologists, not the least important of the many contributions of these 

 authors to our knowledge of the Trypanosomes. Even as it is, the line of 

 demarcation between forms which are to be regarded as typical and repre- 

 senting a phase in the life-history, and those wliich are abnormal and 

 commencing to degenerate, is often sufficiently difficult to draw. 



Trypanosomes appear to be, in most cases, able to support, for a longer or 

 shorter period, unfavourable conditions of environment, whether due to the 

 reaction of the host itself, or to the transference of the parasites to a strange 

 medium. Moreover, although the organisms, sooner or later, feel the effects 

 of such altered circumstances and show signs of involution, it by no means 

 follows that they rapidly die off. On the contrary, a great number of these 

 abnormal forms, on entering the blood of a fresh host, are able to infect it, 



