D. Keilin 
221 
small micronucleus is borne. In a few individuals, I was still able to perceive 
the faint superficial striation of the protoplasm and one or two basophile 
vacuoles. Several cysts showed a clear vacuole ranging from 3p, to 8/x in 
diameter. The wall of the cyst is very thin and does not show any definite 
structure. 
From the foregoing, it is evident that the parasite passes through a period 
of rapid multiplication within the body of the Stegomyici larva, after which 
Fig. 5. Larva of Steg'omyia scutellaris Walker, posterior end of the body showing by transparency 
several specimens of active stages of Lambornella stcgomyiae , L. and many cysts of this 
ciliate, Cys., fixed upon the cuticle of the larva. 
it leaves its host and fixes itself on the external surface of the cuticle (and, 
possibly, to any adjacent solid object), and there becomes encysted. The para¬ 
sites probably leave the body of the host through artificial ruptures of the 
body-wall, and as the gills are the most fragile of the appendages of the larva, 
it appears to be likely that the parasites reach the exterior through the openings 
which are left after the gills have broken away (see Lamborn, p. 214). In 
connection with this, it is interesting to note that larva No. 4, which was 
covered with cysts of Lambornella , had lost two of its gills. 
