STATE GEOLOGIST. V 



about the pathological conditions prevailing among such lowly 

 animals, but it can be shown that these same causes of disease may 

 not be unimportant in connection with human diseases. 



Tt is a fact constantly receiving new exemplification, that the 

 parasites infesting small animals, particularly water animals, are 

 frequently but the immature forms of parasites of animals higher 

 in the scale. These alternating generations are exceedingly diffi- 

 cult to study, so that while all stages may be separately known, 

 only a fortunate combination of circumstances or patient accumu- 

 lation of facts can connect the individual factors into the complete 

 cyclus. 



Thus, for example. Prof. Leuckart has but recently worked out 

 the full life-history of Distomum hepaticum, although the adult 

 has been a stock example in helminthological study in the labor- 

 atory for years. 



The importance of such parasites, even in a commercial view, 

 needs but a reference to trichinosis to illustrate. I am not aware 

 that endo-parasites are known in entomostraca except in the case 

 of Cyclops. Embryos of Cucullanus elegans, a nematoid worm, 

 enter the body cavity of cyclops and undergo two moults and then 

 are transferred to the intestinal canal of food fishes.^ 



A similar parasite of cyclops is Filaria medinensis.'^ 



The cladocera are generally quite free from parasites, but I have 

 found in several instances young nematoids m the blood sinus in 

 front of the heart in Daphnia schcefferi. These worms subsist 

 upon the nutriment m the blood which constantly bathes the 

 animal. True cysts could not be formed in the cobweb-like tis- 

 sues of the hosts. This is, so far as I can learn, the first publica- 

 tion of entozoa from cladocera, and the parasites are figured in 

 Plate T, Fig. 15. The animals were from 'Schimels Teich,' Leipzig. 



While collecting copepods near Tuscaloosa, Ala., I gathered a 

 number of specimens of Cyclops tenuicornis, and nearly all were 

 unusually pale and feeble, (^n examination they proved to be in- 

 fested with a worm of the sub- order Distomese. 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 attained." 



"The larvae live frequently in moUusca, and in maturity 

 inhabit the intestine of vertebrates. 



Upon examination, the cyclops individuals collected were nearly 



iClaus. Kleines Lehrbuch d. Zoologie, p. 368. . .," 



2Fedsclieulio. Ueber d. Bau. u. d. Entwicklung d. Filaria medmensis, Moscow. 



