1883.] Heterogenetic Development in Diaptomiis. 387 



Entomostraca, the significance of these facts cannot fail to appear. 

 A similar parasite of Cyclops is FtlaiHa inedinensis} 



The Cladocera are generally quite free from parasites, but I 

 have found in several instances young nematoids in the blood 

 sinus in front of the heart in Daphnia magna. These are mouth- 

 less but very active round worms, subsisting upon the nutriment 

 in the blood which constantly bathes the animal. True cysts 

 could not be formed in the cobweb-like tissues of the hosts. 



This is, so far as I can learn, the first publication of Entozoa 

 from Cladocera. The animals were from " Schimels Teich," 

 Leipzig. While collecting Copepods near Tuscaloosa, Ala., I 

 gathered a number of specimens of Cyclops teniiicornis and nearly 

 all were unusally pale and feeble. On examination they proved 

 to be infested with a worm of the sub-order Distomeae. This 

 sub-order includes many distressing parasites and forms which are 

 adapted to be widely distributed by a long period of adolescence 

 and the number of stages passed through before maturity is at- 

 tained. 



The larvae live frequently in Mollusca, and in maturity the ani- 

 mal inhabits the intestine of vertebrates. 



Upon examination the Cyclops individuals collected were nearly 

 all found affected, some having as many as five parasites of vari- 

 ous sizes about the alimentary canal, in the common vascular 

 cavity which corresponds to the entire arterial and venus system 

 of the more highly organized Calanidae. The Cercarian or tailed 

 stage was not found. Were the life-history known it would prob- 

 ably appear that the larval stage is passed within some young 

 moUusks, and that the adult infests some vertebrate, probably fish, 

 and would thus be perhaps transferred either in food or drink to 

 human system. 



It is worthy of notice that the host was soon destroyed by the 

 parasite, the post-imago or Coronatus form being absent ; most of 

 the individuals thus infested possessed abnormally persistent lar- 

 val characters in antenna, etc. 



EXPLANATION OF PLATE V. 



Fig, I, Diaptomus castor {?), fifth pair of legs of adult male. 

 " la. " same (older specimen) showing a greater retrograde 



metamorphosis of inner ramus. 

 "2. " caudal stylets of adult. 



' Fedschenko. Ueber d. Bau. u. d, Entwicklung d. Filaria medinensis, Moscow. 



