TWELFTH AKKUAL EEPOKT. 



CHAPTER I. 



THE ENEMIES OF ENTOMOSTRACA. 



First among these rank the young of various fishes which prey 

 upon, and find their entire support in, these minute animals. This 

 subject has been fully treated by Forbes, Ryder and others. 



The enemy next most dreaded by entomostraca is, perhaps, the 

 "spectre animalcule" or the larva of the little frost-gnat, corethra. 

 It is no unusual thing to see a corethra carefully gorging itself 

 with a fat cyclops, suddenly seized by the protractile jaws of the 

 dragon-fly larva, shaken for a minute and then engulfed in the 

 tomb-like cavernous mouth below. Nor is the road to the 

 stomach of the dragon-fly always so circuitous. Water-tigers also, 

 with other larvae, prey upon these unfortunates. The hydra con- 

 siders them a dainty morsel, and at once paralyzes them by the 

 touch of his nematocystiferous arms; in other words, by the pois- 

 onous barbs coiled in concealment in the cells of the tentacles. 



If the animal flys from these ubiquitous enemies he almost cer- 

 tainly is betrayed by carnivorous plants which abound in all our 

 waters. Forbes says: "In ten bladders of UtricidmHs tmlgaris^ taken 

 at random, I found 93 animals, either entire or in recognizable 

 fragments, and representing at least 28 species. Seventy-six of 

 the animals found were entomostraca, and belonged to 20 species." 

 "Just one-third of all the animals found in these bladders belonged 

 to the single species Acroperus leucocephalus^ Koch." 



But among the ranks of enemies must be included certain para- 

 sites, both external and internal, of which a variety are known. 

 A few of the most remarkable of these will be mentioned. I may 

 be permitted to quote from an article in the American Naturalist, 

 April, 1883: 



"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 



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