402 THE BIOLOGY OF HYDRA : 1961 



as H. littoralis. All organisms in the clone were found to be infected 

 with Microsporidia, the parasitization occurring in both the epider- 

 mal and gastrodermal cells. Treatment of the Hydra with a fungi- 

 cide, Fumidil B, apparently eradicated the parasite as clones of 

 the treated Hydra have remained parasite-free for two years. These 

 Microsporidia have been identified tentatively through the courtesy 

 of Dr. R. R. Kudo as a species of Plistophora — a type of protozoal 

 parasite causing fatal infections of silkworms and honeybees. Re- 

 ported for the first time in Hydra, the infection in this organism is 

 not fatal, nor does it interfere with normal asexual reproduction. 

 Because of this, parasitized Hydra may provide a unique system 

 for the study of the life cycle of Microsporidia (7). 



Hydra littoralis — Strain II: These were from a clone generously 

 furnished ])y Dr. Loomis and identified as H. littoralis. 



Hydra littoralis — Strain III: In an effort to obtain a non- 

 parasitized Hydra closely resembling Strain I, a sexual cross was 

 made between an infected male of Strain I and a female of Strain 

 II. The resulting offspring were parasite-free. These clones have 

 been designated Strain III. (When the opposite cross was made, 

 the eggs hatched only rarely and the offspring were infected. ) 



Hydra littoralis — Strain IV: Another clone, referred to as 

 Strain IV, was developed from a Hydra found in a pond on the 

 University of Texas campus and has been tentatively identified 

 through the courtesy of Dr. L. H. Hyman as H. littoralis. 



The two strains (I and IV) only tentatively identified as H. 

 littoralis have been considered as members of this species in view 

 of their close morphological resemblance to the positively identi- 

 fied Strain II and because of the readiness with which Strains I and 

 IV cross sexually with Strain II to produce \'iable offspring which 

 later become sexually reproductive. Although all four strains ap- 

 pear to be Hydra littoralis, there is variation in size, rate of regenera- 

 tion, and physiological responses. Strains I, II, and III are all very 

 much alike in appearance but Strain IV is a larger and a more 

 slowly moving Hydra. 



Hydra oligactis: These are from clones developed from an or- 

 ganism purchased from General Biological Supply Co., Chicago, 111. 



Chlorohydra viridissima (Green): This culture of Chlorohy- 

 dra was derived from specimens found in a local pond. 



