1900.] on Malaria and Mosquitoes. 11 



scare in Bengal still rendered observations with the human species 

 almost impossible. By feeding Culcx fatigans on birds with II. relicla 

 and then examining the insects one, two, three and more days 

 afterwards, it was easy to trace the gradual growth of the zygotes. 

 Their development briefly is as follows : After the fertilisation of the 

 macrogamete has taken place in the stomach-cavity of the gnat, the 

 fertilised 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 cell " that is, a little oval body, about 

 the size of a large red corpuscle or larger, and containing the granules 

 of melanin possessed by the parent gametocyte from which the macro- 

 gamete 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 six 

 days, if the temperature of the air be sufficiently high (about 80 F.), 

 the diameter of the zygote has increased to about eight times what it 

 was at first ; that is, to about 60 /z. If the stomach of an infected 

 insect be extracted at this stage, it can be seen, by a lower power of 

 the microscope, to be studded with a number of attached spheres, 

 which have something of the appearance 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 

 mentioned ; 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 1^-16 /j. in length, of extreme delicacy, and somewhat 

 spindle-shaped that is, tapering at each extremity. Just as the 

 zygotes recall the shape of the Coccidiidas, so do these blasts recall 

 the "falciform bodies." 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 polyembryony. Just as a fertilised ovum gives rise 

 to blasts which produce the cluster of cells constituting a multi- 

 cellular animal, so, in this case the fertilised ovum or zygote gives 

 rise to blasts, each of which, however, becomes a separate animal. 



