Insects and Disease 
625 
since these are so extremely like each other. I elected to work with the 
avian species, chiefly because the plague-scare in Bengal still rendered obser¬ 
vations with the human species almost impossible. By feeding Culex 
fatigans on birds with' H. relicta and then examining the insects one, two, 
three or more days afterwards, it was easy to trace the gradual growth of 
the zygotes. Their development briefly is as follows: After the fertilization 
of the macrogamete has taken place in the stomach-cavity of the gnat, the 
fertilized parasite or zygote has the power of working its way through the 
mass of blood contained in the stomach, of penetrating the wall of the organ, 
and of affixing itself on, or just under, its outer coat. Here it first appears 
about thirty-six hours after the insect was fed, and is found as a ‘pigmented 
celT—that is, a little oval body, about the size of a large red corpuscle, and 
containing the granules of melanin possessed by the parent gametocyte 
from which the macrogamete originally proceeded. In this position it shows 
no sign of movement, but begins to grow rapidly, to acquire a thickened 
capsule, and to project from the outer wall of the stomach, to which it is 
attached, into the body-cavity of the insect-host. At the end of s'x days, if 
the temperature of the air be sufficiently high (about 8o° F.), the diameter 
of the zygote has increased to about eight times what it was at first; that is, 
to about 60 microns. If the stomach of an infected insect be extracted at 
this stage, it can be seen, by a low power of the microscope, to be studded 
with a number of attached spheres, which have something of the appear¬ 
ance of warts on a finger. These are the large zygotes, which have now 
reached maturity and which project prominently into the mosquito’s body- 
cavity. 
“All this could be ascertained with facility by the method I have men¬ 
tioned: and it should be understood that gnats can be kept alive for weeks 
or even months by feeding them every few days on blood, or, as Bancroft 
does, on bananas. But a most important point still required study. What 
happens after the zygotes reach maturity? I found that each zygote as 
it increases in size divides into meres , each of which next becomes a blastophore 
carrying a number of blasts attached to its surface. Finally, the blastophore 
vanishes, leaving the thick capsule of the zygote packed with thousands 
of the blasts. The capsule now ruptures , and allows the blasts to escape 
into the body-fluids of the insect. 
“These blasts, when mature, are seen to be minute filamentous bodies, 
about 12-6 jj. in length, of extreme delicacy, and somewhat spindle-shaped— 
that is, tapering at each extremity. Prof. Herdman and I have adopted 
this word ‘blast’ for these bodies after careful consideration, but others 
prefer other names. They are, of course, spores; but spores which have 
been produced by a previous sexual process, and are in fact the result of 
a kind of polembryony. Just as a fertilized ovum gives rise to blasts, 
