HYPOBIOSIS IN PARASITIC WORMS 10 1 



suitable food source, where the larvae drop, start feeding, 

 become mature and multiply normally^^. 



ENCYSTED LARVAE 



The fully developed larvae of parasitic worms either enter 

 actively or are transferred passively (free or included in eggs) to 

 a suitable host. In the final or definitive host they develop to the 

 adult stage. In the intermediate host practically all parasitic 

 worms — some nematode species are excepted — encyst and 

 become transformed into a higher resting larval stage. Such 

 larvae of trematodes appear as metacercaria, of cestodes as 

 cysticercus or plerocercoid, of acanthocephala as acanthor, of 

 nematodes as agamospirura, etc. All these stages are in a state 

 of dormancy which either ends when the intermediate host is 

 swallowed by the definitive host, or the larvae die if quiescence 

 is prolonged. The life span of the encapsuled stages of the 

 helminths varies greatly; in some instances it may last for years. 

 Usually the larvae encyst in a specific organ or tissue. Sometimes, 

 however, they may establish themselves anywhere in the body. 

 In most instances the encapsuled larvae do not change; they 

 absorb just enough food from their host's tissues to maintain 

 their state. In some cases, however, the encapsuled larvae grow 

 and expand. The larva of the cestode Echinococcus granulosus, 

 the hydatid, may develop in various mammals and in man to the 

 size of a child's head and produce serious impairment of health. 



The larvae of the nematode Rhabditis maupasi* exhibit 

 quiescence in peculiar circumstances. They live in their free- 

 living Stage in the soil, until they are swallowed by an earth- 

 worm. In the latter they partly remain active but without 

 change in the protonephridia and partly encysted in various 

 tissues. The latter part of the larvae apparently play the main 

 role in propagation of the species. They remain quiescent 

 as long as the host lives or until it autotomizes the hind 



* Syn. Rhabditis pellio sensu Buetschli, 1873, nee Schneider, 1866 (14). 

 References p. 106 



