194 



THE HARM OF LA CELL A TES 



it is invariably attached in this manner, but the flagellum is 

 probably not homologous in all these cases. In certain Trypano- 

 somes which are to be derived from a Monadine ancestor, it is, of 

 course, the single flagellum that is represented, with the free part 

 directed anteriorly ; other forms, however, are rather to be looked 

 upon as derived from a Heteromastigine ancestor, the flagellum 

 that persists being the trailing, posteriorly directed one (the 

 so-called " Schleppgeissel"). 1 There are two nuclear bodies, one, 

 the trophonucleus, regulating the trophic life of the cell, the other, 

 the kinetonucleus, directing its locomotor activities. 



FIG. 1. 

 " Undulina ranarum," Lankester, 1871. In 13 the nucleus is shown. 



The most general method of reproduction is by binary, longi- 

 tudinal fission ; but multiple division or segmentation is also met 

 with. As regards the life-cycle of the parasites, only little is as 

 yet known in most cases. From the results of the most recent 

 researches, however, it certainly appears probable that, apart from 

 various blood - sucking Invertebrates which may (mechanically) 

 transmit a given parasite, there is, in general, a true alternate host 

 for each form ; one, that is, in which definite phases of the life- 

 cycle including, most likely, sexual conjugation are normally 

 undergone. Further knowledge on this subject is greatly needed. 



Historical. The first observation of a Trypanosome is probably 

 to be ascribed to Valentin, who, in 1841, announced his discovery 



1 This flagellum is also termed the gubernaculum (see p. 159). 



