500 



NATURE 



[March 27, 1902 



to be those which it passes in the human blood. In reality its 

 mature condilion and most important motile, as well as ils most 

 prolific reproductive, phases are passed in the body of the 

 mosquito. 



(1) The malaria-germ which is brought by the stab of the 

 Anopheles into the human blood-vessels is a reproductive 

 particle, a spore. It is needle-like in shape, and might be named 

 in reference to its form (e.g. oxyspore or raphidiospore), but the 

 most important fact about it for description and comparison is 

 that it has been formed outside the human body, and is intro- 

 duced as a strange element into the human blood by the agency 

 of the mosquito. I therefore call it the Kxotosi'Ore. 



(2) The Exotospores (probably as many at a time as forty or 

 fifty) enter the blood by the agency of the mosquito's stab and 

 immediately penetrate, each one, a red corpuscle. The history 

 of this process has not been observed. As soon as it has entered 

 a red corpuscle the exotospore losss its needle-like shape and 

 becomes amrebiform. I apply to it the name I proposed some 

 years ago for similar amccbiform spores in other Protozoa, 

 namely, AMa:BULA (" Encyclopaedia Britannica," article 

 " Protozoa"). 



(3) The Amoebula exhibits amceboid movements within the 

 red corpuscle, enlarges and finally breaks up into spherical 

 spoies, which are liberated with destruction of the red corpuscle. 

 It seems to me unnecessary to have a special name for the star- 

 like or other condition of the Annebula when in course of 

 breaking up into spores ; but the spores so produced require a 

 special name which shall emphatically distinguish them from 

 the Exotospores. I call them the ENH.tMOsrORES, in reference 

 to the fact that they are produced by a process of division which 

 occurs in the blood of the malaria-stricken human being. 



(4) The Enhsemospores penetrate /resh red blood-corpuscles, 

 and after a certain growth as amajbuk-e break up into a new crop 

 of Enhremospores, by which the infection of the red corpuscles 

 is extended. This process appears to go on for several genera- 

 tions and for a varying duiation of time. But owing to con- 

 ditions and at a period of the infection which has not been 

 precisely ascertained, some (or all?) of the amrebulce derived 

 from Enhreniospores cease to break up into spores. Instead of 

 carrying out that process they enlarge, and in the case of the 

 sestivo-autumnal parasite {Laveratiia praeeo.x) become sausage- 

 shaped or, as it has been termed, crescent-shaped. This change 

 of form is accompanied by a destruction of the red corpuscle and 

 the formation of granules of dark pigment within the parasite. 

 It seems best to term this phase the "cre;scent'' or "crescent- 

 SPHERE," the latter term being applicable to those species in 

 which the form is not markedly crescentic. 



(5) The crescents or crescent-spheres remain quiescent in the 

 human blood. They are, however, of two different natures — 

 male and female. It is not possible to distinguish with any 

 certainty the male from the female crescents whilst they remain 

 in the human blood-vessels. But it is these bodies which ar6 

 destined to be swallowed by the Anopheles mosquito and to 

 carry on further the life-history of the parasite. 



The crescents are therefore the sexual phase of the parasite. 

 When the crescents are swallowed by a mosquito (of an appro- 

 priate species), they undergo two different modes of develop- 

 ment, determined by the fact of their sex. Both sexes become 

 spherical, and may now be called respectively " ECG-CELL " 

 and " .SI'ERM-MOl HER-CEI.L." 



From the periphery of the sperm-.mother-cei.i., now floating 

 in the mosquito's stomach, there are developed with surprising 

 rapidity six or seven spermatozoa, which for a time remain 

 attached to the residual mass (or sperm-ui.astopiior) of the 

 sperm-mother-cell. Complete cytological study of this develop- 

 ment 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, 

 apparently gives rise to one, and possibly to two, polar bodies, 

 but the observations on this point are, as yet, insuftlcient. 



Eertilisation of the egg-cell now lakes 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 prodi'CED e.mbryo remains 

 unicellular, but increases in size and becomes pyriform. It 

 exhibits active movements of expansion and contraction in the 



NO. I 69 1, VOL. 65] 



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 presented by the life- 

 history of the malaria parasite. It has been called "vermi- 

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

 viz. the Vermiculk. The vermicule is the dominant indi- 

 vidual form in the history of the malaria parasite, endowed with 

 greater size, power and activity than other phases. It corre- 

 sponds, not only in this respect, but also in ils 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 

 (" Encyclop.-edia Britannica," article " Protozoa"). 



It is worthy of note that in the size and activity of the vermi- 

 cule, the IL-emaosporidia — the order of Sporozoa which em- 

 braces the malaria parasite — come nearer to the Gregarinidea 

 than they do to the Coccidiidea, though in the existence of a 

 sexual generation absent in Gregarinidea they agree with the 

 Coccidiidea.' 



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 delinite process 

 to form eventually an immense number of exoto.spores, 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 re- 

 lation to the quiescence of the organism and its division into 

 numerous reproductive spores. Unfortunately, the word " sporo- 

 cyst " has been employed recently by writers on the Sporozoa 

 for the small capsules containing one or two to eight elongated 

 spores which used to be called " pseudonavicul.^," and are 

 formed within such larger cysts as that now in question. The 

 word "cyst" should have been reserved for the larger more 

 general protective envelope, and the " pseudonavicula- " might 

 have been called " sporo-thek«:s." In any case, I think we 

 may call the cysts in which the vermicules of the malaria para- 

 site enclose themselves "spore-cysts" or " spore-for.ming 

 CYSTS." The name "oocyst," applied to them by some 

 writers, is simply misleading. 



(7) The spore-cysts lying Outside the stomach wall of the 

 mosquito bathed in the insect's blood receive abundant nourish- 

 ment. The single-celled vermicule enclosed undergoes rapid 

 changes; it increases greatly in volume and breaks up by normal 

 cell division (? the earliest steps have yet to be studied) into a 

 number of sfore-.mother-cei.ls. In the process of this 

 division and the later stages of the final development of the 

 "spores' (exotospores), the "spore-forming cyst" increases in 

 size to twenty times its initial diameter. 



The spore-mother-cells are set closely together in the cyst v 

 they are of polygonal shape, owing to pressure, and each has its 

 nucleus. Finally they give rise, each sp,)re-mother-cell, to a 

 crop of filiform spores (exotospores) which have the same 

 relaticm to the spore-molher-cell as spermatozoa have to a sperm- 

 mother-cell, viz., they form on the outside of the spore-mother- 

 cell as outstanding processes, carrying away all the chromatin of 

 the mother-cell and leaving in the centre or to one side a 

 " residuary body," a " spore blastophore" similar to the " sperm- 

 blastophore" of spermatozoon- development. 



Thus we are brought back to the needle like exotospores with 

 which we started. 



The spore-holding cysts burst and liberate the exotospores 

 into the blood of the mosquito. Thence they readily pass into 

 the ducts of the salivary gland, and so are conveyed by the 

 mosquito's stabbing beak into human beings. A point in this 

 connection is the definite ejection by the mosquito of the secretion 

 of its salivary gland into the punctured wound which it makes 

 in the human skin. There can be no doubt that such an ejection 

 takes place. The leech ejects a secretion on to the wound 

 caused by its bite which has the property of preventing the 

 coagulation of the blood. It is possible that the mosquito and 

 other blood-sucking flies may use the salivary secretion for the 

 same purpose. It is obvious that unless there were some 

 injection into the wound on the part of the fly, the chances of 



1 A sexual phnse has been described in the GreE.-Kine Stylorhynchus by 

 L(<ger since this paper was written. It occurs at an unevpecled point i 

 cycle: two encysted full grown '*Sporonts 

 egg-cells the otner spermatozoids. 



stated to produce the one 



