OE ANIMALS WITHOUT BLOOD. 221 



that it would include most animals of the sub-kingdoms 

 Arthropoda, Vermes, and Echinodermata, but this definition 

 is so qualified by other passages in his works as to show that 

 the meaning which he gave to the term, in practice, was of 

 very much narrower scope. His Malakostraka, among 

 which he included many crustaceans, constitutes a separate 

 genos or class ; * he expressly excludes from his Entoma 

 animals which are not furnished with many legs, and adds 

 that the number of legs is proportional, in some way, to the 

 length of the body or number of its incisions, a smaller 

 number of legs being compensated for by the presence of 

 wings, t His Entoma, in fact, are chiefly butterflies and 

 moths, beetles, bees, wasps, hornets, ants, houseflies, gad- 

 flies, gnats, dayflies, grasshoppers, locusts, spiders, scor- 

 pions, centipedes, and millipedes. 



As far as he separated crustaceans from his Entoma, 

 Aristotle was greatly in advance of many of the later 

 naturalists, who classed them with their Insecta. Agassiz 

 says : — "Aristotle divides this group more correctly than 

 Linnaeus, as he admits already two classes among them, the 

 Malacostraca (Crustacea) and the Entoma (Insects). "t 

 The confused classifications of the lower forms of life 

 adopted by naturalists of the sixteenth, seventeenth, and 

 eighteenth centuries were chiefly due to their adoption 

 either of Aristotle's definition of his Entoma, without any 

 regard for its qualifying clauses, or Pliny's definition, § 

 which is adapted from Aristotle's definition but includes 

 apterous and also apodal animals which have incisions. 



Aldrovandi, Swammerdam, Ray, Linnaeus, and many 

 others included, in their writings on " insects," crustaceans 

 and some other forms of life which Aristotle's Entoma 

 would not include. However, at the very beginning of the 

 nineteenth century, Lamarck definitely separated the 

 Crustacea and also the Arachnida from his Insecta, and, 

 although he kept an old order, Insecta aptera, he deprived 

 it of most of its former dignity by assigning to it only one 

 genus, viz., Pulex, Linn., with two species, of which one is 

 P. irritans, or " la puce ordinaire." || To discuss satisfac- 

 torily the classifications of "insects" made between the 

 time of Aristotle and that of Lamarck would be a task of 



■■■■ H. A. i. c. 6, s. 1, iv. c. 1, s. 2 ; G. A. i. c. 14, 7206. 

 + P. A. iv. c. 6, 682a and b. 



I An Essay on Classification, 1859, p. 305, Note. 

 § Nat. Hist, xi, 1. 



II Syst. des Aiiim. sans Vertebr,, Paris, 1801, p. 314. 



