686 H. M. WUODCOCK. 



Certain other phases or developmental forms of the trypa- 

 nosomes, however, have been encountered in cultures which 

 were in a normal healthy conditiou, but these have been, 

 as a rule, scanty in number, contrasting markedly with 

 the abundance of the prevailing types. In cultures of 

 six or seven days' age or more a small percentage of the 

 individuals — and usually only a very small percentage — show 

 a tendency to lose the fusiform or more active type of form, 

 and to develop a pear-shaped or rounded, more passive type 

 of form. In most of my culture-series (including sub- 

 cultures), these pyriform or ovoid forms are very infrequent 

 and have to be carefully searched for, even on slides where the 

 ordinary parasites are most abundant. The individuals of 

 this character are generally of medium, or less than medium 

 size, but occasionally are large and massive. Pear-shaped 

 forms are seen in figs. 112-114, that of hg. 113 being from a 

 redpoll culture, the others from different chaflBnch ones. The 

 dimensions of these parasites (Hagellum excluded), are, for 

 example, 8 fi by 5 /i (fig. Ho), and 6^/1 by 3f /« (fig. 114), 

 Medium-sized ovoid forms are 8/i by 6/x (figs. 116 and 117). 

 The large ovoid individual of fig. 118 is 13yu by 7ju and has 

 a very long flagellum ol 24 fx; the small corresponding form 

 (hg. 115), is 6 fi by 4ju. Although I have distinguished 

 these parasites as more " passive " forms, it is difficult to 

 know whether to regard them as being about to enter on a 

 " resting-phase," for in all cases where 1 have observed them 

 in what were normal, healthy cultures, these individuals 

 possessed a flagellum. I may mention here that the only 

 instance where I have found rounded-ofl: parasites which 

 lacked a Hagellum was in a culture (original), nineteen days 

 old, which was full of atypical, altered forms (cf. below, 

 p. 696). 



This type of parasite, whether pyriform or ovoid, to 

 rounded, is almost certainly to be derived from forms in 

 which the alteration in nuclear position has occurred, and in 

 which the modified method of multiplication, by unequal fission, 

 has made its appearance. Pear-shaped individuals, such as 



