Laveran had early suggested that the rôle of carrier might be played by the mosquito, but Manson first clearly formulated the hypothesis, and it was largely due to his suggestions that Ross in India, undertook to solve the problem. With no knowledge of the form or of the appearance in this stage, or of the species of mosquito concerned, Ross spent almost two and a half years of the most arduous work in the search and finally in August, 1897, seventeen years after the discovery of the parasite in man, he obtained his first definite clue. In dissecting a "dappled-winged mosquito," "every cell was searched and to my intense disappointment nothing whatever was found, until I came to the insect's stomach. Here, however, just as I was about to abandon the examination, I saw a very delicate circular cell, apparently lying amongst the ordinary cells of the organ and scarcely distinguishable from them. On looking further, another and another similar object presented itself. I now focused the lens carefully on one of these, and found that it contained a few minute granules of some black substance, exactly like the pigment of the parasite of malaria. I counted altogether twelve of these cells in the insect." Further search showed that "the contents of the mature pigment cells did not consist of clear fluid but of a multitude of delicate, thread-like bodies which on the rupture of the parent cell, were poured into the body cavity of the insect. They were evidently spores." With these facts established, confirmation and extension of Ross's results quickly followed, from many different sources. We cannot trace this work in detail but will only point out that much of the credit is due to the Italian workers, Grassi, Bignami, and Bastianelli, and to Koch and Daniels. It had already been found that when fresh blood was mounted and properly protected against evaporation, a peculiar change occurred in these crescents after about half an hour's time. From certain of them there were pushed out long whip-like processes which moved with a very active, lashing movement. The parasite at this stage is known as the "flagellated body." Others, differing somewhat in details of structure, become rounded but do not give off "flagella." The American worker, MacCallum (1897), in studying bird malaria as found in crows, first recognized the true nature of these bodies. He regarded them as sexual forms and believed that the so-called flagella played the part of spermatozoa. Thus, the "flagellated body" is in reality a _microgametoblast_, producing _microgametes_, or the male sexual element, while the others constitute the _macrogametes_, or female elements.