DEFINITION OF THE TERM INSECT. 17 



many. The majority couple often in the course of life*." 

 I shall next add his definition of Crustacea : " Ovipa- 

 rous, articulated, apterous animals, with a crustaceous in- 

 tegument more or less solid, having jointed legs ,• eyes 

 either pedunculate or sessile, and most commonly four 

 antenna:, with a maxilliferous mouth seldom rostriform ; 

 maxilla: in many pairs placed one over the other ; scarcely 

 any under-lip ; no spiracuhform openingsfor respiration ,• 

 five or seven pair of legs ,• a longitudinal knotty marrow 

 terminated anteriorly by a small brain. A heart and ves- 

 sels for circulation. Hespiration branchial with external 

 branchicc, sometimes hid under the sides of the shell of the 

 thorax, or shut in prominent parts ; sometimes uncovered, 

 and in general adhering to partiadar legs or to the tail t 

 Each sex usually double^." 



I have given Lamarck's definitions of these three classes, 

 all considered as Insecta by Linne, that by comparing 

 them together you may be better enabled to appreciate 

 the system of this author. On looking over the characters 

 of the Arachnida as here given, you will see at once that 

 it consists of heterogeneous animals — for in fact he in- 

 cludes in this class not only the Trachean Arachnida of 

 Latreille, but the Ametabolia of Dr. Leach, or the Hexa- 

 pod Aptera, and the Myriapoda. 



I shall next copy for you Latreille's latest definition of 

 Insecta and Arachnida. 



" Insecta : A single dorsal vessel representing the 

 heart : two trunks of trachea running the whole length 

 of the body, and opening externally by numerous spira- 

 cles; two antenncB ; very often upper appendages for 

 flight, indicating the metamorphosis to which the animal 



* Anim. tans Vertebr. iii. 245. b Ibid. 



VOL. III. C 



