362 THE PROTOZOA 



have, according to Schaudinn (130), no signet-ring stage in their 

 development, but are of compact form, and grow more slowly than 

 the trophozoites which become schizonts. The sporonts are of 

 two types, male and female (Fig. 156, Villa., VIII6.) ; the male 

 forms have a large nucleus and lightly-staining, clearer cytoplasm ; 

 the female forms have a smaller nucleus and more deeply staining 

 cytoplasm. In the tertian and quartan parasites the sporonts are 

 distinguishable from the schizonts by their greater size and more 

 abundant pigment in larger grains. In the parasite of pernicious 

 malaria, the sporonts are further characterized by their sausage- 

 like form (Fig. 166, Vila., VII6.), and are thereby easily dis- 

 tinguishable from the rounded schizonts. 



The sporonts only undergo further change if taken up by a mos- 

 quito of a species capable of acting as the specific host of the para- 

 site. When human blood containing various stages of the parasite 

 is ingested by a culicine mosquito, all stages of the parasite are 

 digested with the blood ; but if taken up by an anopheline, the ripe 

 sporonts resist the action of the digestive juices of the mosquito, 

 and develop further in its stomach, while all other stages succumb. 

 The sporonts burst the corpuscle in which they are contained, and 

 round themselves off. In the male sporont the nucleus undergoes 

 rapid fragmentation into some four or six nuclei (Fig. 156, IXa.), 

 leaving a residual karyosome at the centre of the body, as in 

 Coccidium (Schaudinn, 99). The daughter-nuclei place themselves 

 at the surface of the body, and grow out with explosive suddenness 

 into fine filaments of chromatin, ensheathed in a scarcely perceptible 

 layer of cytoplasm (Fig. 156, Xa.). Each such filament is a micro- 

 gamete, of slender, spirochaete-like form, without flagella, but 

 endowed with powers of active movement. The microgametes 

 lash about violently, often dragging the body of the sporont after 

 them, and presenting a superficial resemblance to flagella, which, 

 indeed, they were formerly thought to be ; hence the process of 

 microgamete-formation, which can be observed without difficulty 

 in freshly-drawn blood, was thought to represent a flagellated 

 " Polymitus " stage of the parasite, and was termed " exflagella- 

 tion." The microgametes by their movements finally become 

 detached, and swim away from the body of the sporont, which 

 perishes as residual protoplasm. 



In the female sporont the nucleus divides to give off a reduction- 

 nucleus (Fig. 156, X6.) ; it is then ripe for fertilization by a micro- 

 gamete (Fig. 156, XI.), which penetrates the body and fuses with 

 the female pronucleus. The zygote then changes from a rounded 

 form into an elongated vermicule, termed an " ookinete " (Fig. 156, 

 XII., XIII.), which moves by gliding movements, like a gregarine. 

 The ookinete bores its way through the lining epithelium of the 



