192 H. M. WOODCOCK. 



accumulation of reserve material, and the parasite's dimeu- 

 sions may attain thrice those of an indifferent Trj^panosorae. 

 The older forms are no longer able to pass from the passive 

 into the active condition, and can only perform slow movements 

 of contraction, flexion, and the like. 



In consequence of their i-eserve stores the adult females, in 

 the gregariniform phase, are exceptionally resistant to ex- 

 ternal influences, and the most able to withstand unfavourable 

 circumstances. During long hunger-periods of the gnat all 

 the other stages of the parasite die off. Only the females, 

 deeply seated between or beneath the epithelial cells, remain 

 alive, slowly using up their supply of nutriment. With the 

 advent of fresh blood into the stomach they undergo partheno- 

 genesis, at the end of which the parasites are able to become 

 either indifferent, male, or female forms again, the result 

 being that once more fresh generations of Trypanosoraes 

 overrun the alimentary canal. It is, moreover, the gregarini- 

 form females which bring about the infection of succeeding 

 generations of the gnat, remaining dormant in the ovaries 

 throughout the winter until the eggs are laid and the larvce 

 develop in the following spring. 



Parthenogenesis. — The cytoplasm of a parasite about 

 to undergo parthenogenesis is poorer in reserve material, and 

 now more or less vacuolated. No trace of the locomotor 

 apparatus is visible, and the kinetonucleus lies in contact 

 with the trophonucleus (fig. 11 a). The centrosome of the 

 latter is now surrounded by a chromatic body which some- 

 what resembles the kinetonucleus when occupying this posi- 

 tion in the compound nucleus of an ordinary ookinete ^ (cf. 

 figs. 8 A, and 9 a) ; and the whole nucleus next undergoes a 

 process apparently similar to that which occurs in an in- 

 different ookinete at that time. The formation of a hetero- 

 polar spindle leads to the separation of a smaller (kinetic ?) 

 half from a larger half, the latter rapidly reacquiring a 



1 Perhaps this body represents an increase, during the resting-period, of 

 kinetic nuclear constituents, in wliich a female form is apparently more 

 deficient than either a male or an indifferent form. 



