98 THE INVERTEBRATA 



seminal vesicles of earthworms. Several species, some isogamous, 

 others anisogamous. The spores escape either down the vasa defer- 

 entia of the host or by the latter being eaten by a bird, whose faeces 

 contain them intact. Swallowed by another worm, their cases are 

 digested and the sporozoites traverse the intestinal wall to reach the 

 vesiculae seminales, where they enter sperm mother-cells, in which 

 they pass their earlier stages. 



Gregarina (Fig. 80). All three divisions of the body present. 

 Parasitic in the alimentary canals of cockroaches and other insects. 

 The gamocyst develops into a complicated structure with ducts for 

 the discharge of the pseudonavicellae. 



Appendix to the Telosporidia 



Order PIROPLASMIDEA 



Protozoa, parasitic in red blood-corpuscles and transmitted by ticks ; 

 which have no external organs of locomotion; perform agamogony 

 by binary fission; conjugate as hologametes; and after syngamy 

 become motile zygotes which divide in a cyst into numerous, naked 

 sporozoites. 



The members of this group are of doubtful affinity. In the general 

 course of the life-cycle they resemble the Telosporidia, but in the 

 possession by the trophozoite of part of a flagellar apparatus, and 

 in that the gametes are both hologametes, they diff^er from the 

 other members of that subclass. An interesting feature of their 

 life history is that they are transmitted in the ovum from one 

 generation of the invertebrate host to the next. They are at present 

 only known from mammals and ticks. 



Piroplasma { = Babesia). Infests various mammals (cattle, dogs, 

 monkeys) and causes the red-water fever of cattle and other diseases. 

 The trophozoites, in red corpuscles, are pear-shaped and unpig- 

 mented, and have a rhizoplast and basal granule as if for a flagellum. 

 When taken into the alimentary canal of a tick they become gametes 

 and form zygotes, which are ookinetes (p. 91), bore through the gut 

 wall of the host, and reach its ovary. There they enter ova in which 

 they are transmitted to the next generation of the tick. They encyst 

 in the ova and divide into amoeboid sporoblasts (sporokinetes) which 

 are distributed as the cells of the host divide and by their own active 

 migration. Thus some reach the salivary glands. There they become 

 multinucleate and break up into sporozoites, which are injected with 

 the saliva into a new mammalian host. 



