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Prof. E. Kay Lankester. On a Convenient [Feb. 20, 



mass (or sperm-blastophor) of the sperm- mother-cell. Complete 

 cytological study of this development is still wanting, but it appears 

 that the spermatozoa are true spermatozoa, like those of the higher 

 animals, and have the same relation to the mother-cell from which 

 they develop as is the case in such an animal as the Earth-worm. 



The EGG-CELL, now also floating in the mosquito's stomach, appar- 

 ently gives rise to one, and possibly to two, polar bodies, but the obser- 

 vations on this point are, as yet, insufficient. 



Fertilisation of the egg-cell now takes place in the gnat's stomach. 

 A single spermatozoon penetrates and fuses with each egg-cell. 



The fertilised egg-cell is spoken of as a " zygote " ; it is also described 

 as the sexually produced embryo. 



6. The zygote or sexually produced embryo remains unicellular, 

 but increases in size and becomes pyriform. It exhibits active move- 

 ments of expansion and contraction in the line of its long axis, and also 

 a quick movement of its narrower end alternately to either side. This 

 is the largest growth of the individual cell attained to in the series pre- 

 sented by the life-history of the malaria parasite. It has been called 

 "vermiform" and "vermicule " (Ross), and I adopt this name for it, 

 viz., the Vermicule. The vermicule is the dominant individual form 

 in the history of the malaria parasite, endowed with greater size, 

 power, and activity than other phases. It corresponds, not only in this 

 respect, but also in its position in the life cycle, to the large often 

 active cells of the Gregarinidea, which I proposed some time ago to 

 call the Euglena-phase.* 



It is worthy of note that in the size and activity of the Vermicule, 

 the Hsemaosporidia — the order of Sporozoa which embraces the malaria 

 parasite — come nearer to the Gregarinidea than they do to the Cocci- 

 cliidea, though in the existence of a sexual generation absent in 

 Gregarinidea, they agree with the Coccidiidea.f 



The vermicule now pushes its way through the tissues of the gnat's 

 stomach and in the blood sinuses outside the stomach becomes spherical. 

 It enlarges and nourishes itself on the insect's blood, and forms a 

 spherical cyst, or structureless transparent envelope. This cyst is 

 destined to enlarge, with vast increase of its living contents. 



The living cell within the cyst breaks up by a definite process to 

 form eventually an immense number of exotospores, the stage with 

 which the present description commenced. The cyst would most 

 conveniently be called a " sporocyst," since, as so often happens in 

 Protozoa, it is formed purely and simply in relation to the quiescence 



* ' Encycl. Britann.,' Article " Protozoa." 



+ A sexual phase lia-s been described in the Grregarine Stylorhynchus by Leger 

 since this paper was written. It occurs at an unexpected point in the cycle : two 

 encysted full grown " Sporonts " are stated to produce the one egg-cells the other 

 spermatozoids ! 



