40 History of British Entomostraca. 



Ostrapodes corresponds with Latreille's group Ostracoda ; the Cope- 

 podes, with his Carcinoida, the Cladoceres, with his Cladocera, and 

 the Phyllopodes corresponds with his second principal section, the 

 Phyllopa. In this arrangement, therefore, the two last legions of 

 the Maxilles, the Entomostraces and Branchiopodes, correspond ex- 

 actly with Latreille's first order, the Branchiopoda ; and form a 

 very natural group ; whilst the second order, the Faecilopoda, is se- 

 parated altogether from the Entomostraca, properly so called, and 

 correspond with M. Milne-Edwards's sub-classes, Suceurs and Xy- 

 phosuriens. This arrangement I shall adopt in the remarks which 

 follow, and my Catalogue of British " Entomostraca" shall thus 

 be confined to Edwards's two legions Entomostraces and Brachio- 

 podes, or Latreille's Branchiopoda. 



The animals of this group, when noticed in their native habitats, 

 may be seen to have their branchiae constantly in motion, their ac- 

 tion being seldom interrupted. One chief use, therefore, of these lit- 

 tleinsects, in the economy of nature, maybe, as Muller says,* to ven- 

 tilate the water day and night ; and as they chiefly reside in stand- 

 ing pools, they may thus be of great use in preserving them from 

 becoming soon putrid. As this may be considered one of the bene- 

 fits conferred by these insects, it may be useful to know the evils to 

 man they may be likely to produce. Though they are most abundant 

 in stagnant water, they yet occur in considerable numbers in the 

 purer sorts of water that serve as our common drink, and may fre- 

 quently be seen in considerable quantity even in the drinking water 

 of London, Edinburgh, &c; and Muller asserts very gravely, that, as 

 we thus drink them alive and with their eggs, he would not be sur- 

 prised were we to discover them some day in the human intestines.t 

 " Thetime," he says in another place, % " is at hand, when the causes 

 of disease shall not only be sought after in the air, in our method of 

 living, &c. but in the incautious use of waters, often abounding in 

 innumerable animalcules." According to Muller and Straus, these 

 insects live upon vegetable matter and not upon animals ; and the 

 former, in an experiment he instituted, says,§ that in keeping a num- 

 ber of species, such as the Daphnia pennala and longispina, Cypris 

 slrigala and pilosa, Lynceus sphcericus and Cyclops quadricornis, in 

 the same water from the 24th July to the 22d January, during 

 which time the water had evaporated from a depth of five inches to 

 that of one, he frequently subjected small quantities of this water 

 to the microscope, and was never able to discover any animalcules 

 in it upon the most attentive examination, though the intestines of 



* Entomostraca, p. 8. f Ibid. p. 33. \ Ibid. p. 12. § Ibid. p. 7. 



