386 Heterogenetic Development in Diaptomus, [April, 



but both rami are 3 -jointed as in the swimming legs of other 

 Calanidae. On the other hand, regarding both legs as present, the 

 '* hand " of the male does not homologize with the left limb, and 

 we have besides to account for a supernumerary 2-jointed limb on 

 the second joint of the abdomen.. 



The present species was found in large numbers in Mulberry- 

 creek, Cullman count}% Alabama ; the color is bluish-green, and 

 the length about ^^ in, 



Entozoic Parasites in Entomostraca (Fig. 15, PL vi). 



We have discussed the relation of the minute fresh-water Crus- 

 tacea to sanitary science in a paragraph in a recent article in the 

 Naturalist, but it remains to touch upon another phase of the 

 subject. It may be thought unnecessary to trouble ourselves 

 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. 



It 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 scales. These alterating 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, Professor Leuckart has but recently worked 

 out the full life-history of Distomiun Jiepatinim^ although the 

 adult has been a stock example in helminthological study in the 

 laboratory 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 Ciicullamis elegans, a nematoid worm, 

 enter the body-cavity of Cyclops and undergo two molts and then 

 are transferred to the intestinal canal of food- fishes.^ 



Taken in connection with the recent discoveries of S. A. 

 Forbes,^ showing how dependent our own food-fishes are upon 



^Claus. Kleines Lehrbuch d. Zoologie, p. 368. 



2 Forbes. On some Entomostraca of Lake Michigan, A.M. Naturalist, July, 

 1882. 

 Cf. Ryder on Food Fiihes,*Bul. U. S. Fish. Com. 



J 



