232 
Herpetomonas luciliae n. sp. 
Physiology. 
Cytoplasm. The cytoplasm of the miclgut forms shows no differen¬ 
tiation in structure, and therefore its function is probably generalised; 
but in the forms occurring in the ‘crop’ and hindgut, it is more or less 
differentiated into ecto- and endoplasm. The ectoplasm forms the 
periplast, the function of which is doubtless to resist desiccation of the 
cell. It is accordingly most marked in the cysts which, when voided in 
the excreta, have to withstand the effects of atmospheric drying, 
perhaps for long periods. From its structure it seems to be formed 
out of the more solid spongy elements of the cytoplasm. When water 
and food are plentiful, as in the ‘ crop,’ the periplast soon disappears, 
which proves that this structure is ill-adapted for the absorption of 
water and nutritive substances. On the contrary, in the hindgut, where 
the excreta of the fly are more and more concentrated, the periplast is 
rapidly formed. 
The reduced metabolism of the cell is then carried on by the endo¬ 
plasm, acting through the small area which comes to the surface of the 
cell at the ‘cytostome.’ The endoplasm is thus well-named the cyto- 
phaiynx. It seems, from its structure, that this endoplasm is derived 
from the more fluid ‘ hyaloplastic’ part of the cytoplasm. 
Later on, as shown by tbe movements of the chromidia, the ecto¬ 
plasm and endoplasm diffuse into one another, and then the whole 
surface of the cell is available for absorption. The cytostome would be 
a weak spot in the armour of the cell under conditions of excessive 
dryness, were it not for the following changes. As more dryness is 
experienced the cell loses water, thereby causing the cytopharynx to 
retract, and consequently deepening the cytostomic pit. The effect 
of this is to invert the periplastic lips of the cytostome over the vulner¬ 
able area, with the exception of the tiny micropyle described above. 
The cell is thus enabled to withstand prolonged desiccation. 
Rhizoplast. The function of the rhizoplast seems to be the secretion 
of the chromatin filament in the flagellum. This is probably effected 
by the protoplasmic achromatic basis of the rhizoplast. When the 
rhizoplast loses its chromatin this protoplasmic basis is possibly 
retracted into the blepharoplast, in view of the close connection which 
exists between the two structures. 
Flagellum. The flagellum, which, it must be reiterated, consists of 
two distinct parts (i) the protoplasmic basis, and (ii) the chromatin 
