THE SPOROZOA 259 



any length of time one of the voracious leucocytes which wander 

 about." 



The conjugation was first observed by Macallum in the genus 

 Halteridium from birds, and his discovery gave the first clue to 

 the nature of the "flagella," and showed that the "Polymitus" 

 form belonged to the normal cycle of the parasite, in contradiction 

 to the views then prevailing amongst most authorities upon the 

 Haemosporidia, who regarded this phase of the parasite as a 

 process of degeneration. The following is the account of the process 

 of conjugation, and the subsequent formation of the motile zygote, 

 given by Macallum, whose figures are also reproduced here 

 (Fig. 74) : " The two forms [i.e. a granular macrogametocyte 

 and a hyaline microgametocyte] lay at some distance from one 

 another [on the field of the microscope]. . . . The granular form 

 happened to escape from the corpuscle first, and lay perfectly quiet 

 beside the free nucleus and the shadow of the corpuscle. Soon 

 the hyaline body, becoming greatly agitated, burst from the 

 corpuscle and threw out active flagella, which beat about for a 

 few minutes and finally tore themselves loose. . . . One of the 

 four flagella passed out of the field, but the remaining three pro- 

 ceeded directly towards the granular form, lying quietly across 

 the field, and surrounded it, wriggling about actively. One of the 

 flagella, concentrating its protoplasm at one end, dashed into the granular 

 sphere, which seemed to put out a process to meet it, and buried its head, 

 finally wriggling its whole body into the organism, which again became 

 perfectly round. The remaining flagella, seeking to repeat this 

 process, were evidently repulsed, and soon became inactive and 

 degenerated. Immediately on the entrance of the flagellum, the 

 pigment of the organism was violently agitated, without, however, 

 any disturbance of the outline of the organism. Soon all became 

 quiet again, and the period of quiescence lasted about fifteen 

 minutes, when a conical process began to appear at one margin 

 of the organism, which, increasing in size, drew into itself most 

 of the protoplasm, the pigment, to a certain extent, being gathered 

 in the remainder. Finally, most of the pigment was concentrated 

 into a small round appendage, which remained attached to what 

 now had become an elongated fusiform body [the ookinete or 

 vermicule], which soon swam away with a gliding motion." 



The fertilisation has been studied also by Schaudinn in Haemo- 

 proteus and in the tertian parasite, and by Hintze in Lankesterella. 

 In the two former a cone of reception is formed by the macrogamete, 

 but in the latter a fine canal is formed, along which the male 

 pronucleus is guided from the point of entry up to the female pro- 

 nucleus. The zygote resulting from fertilisation is in all cases, 

 apparently, at first a freely-moving gregarine-like vermicule or 

 " ookinete," which seeks out actively, and penetrates, the cells or 



