DEFINITION OF THE TERM INSECT. 19 



horns). Perhaps these last may be regarded as in some 

 sort representing the external antennae of the Crustacea ? 

 With regard to Insecta, their antennas seem to disappear 

 in the PupiparcB Latr., or the genus Hippobosca L. 



The above definitions of the Arachnida by these two 

 celebrated authors, appear to me the reverse of satisfac- 

 tory. When we are told of animals included in it, that 

 some breathe by gills and others by tracheae, that some 

 have a heart and circulation and others not, we are im- 

 mediately struck by the incongruity, and are led to sus- 

 pect that animals differing so widely in the fountains of 

 life ought not to be associated in the same class. A 

 learned zoologist of our own country, Dr. Leach, seems 

 to have made a nearer approach to a classification in ac- 

 cordance with the internal organization, by excluding 

 from Arachnida the Acari and Mijriapoda. 



Sub-kingdom Annulata Cuv. 



* Gills for respiration. Classes. 



Legs sixteen; .... Antennas two or four 1 Crustacea. 



** Sacs for respiration. 

 Legs twelve : .... Antennae none 3 Arachnoidea, 



*** Trachea? for respiration, 

 •a. No Antenna?. 



4 Acari. 



b. Two Antenna?. 



Six thoracic legs : Abdomen also bearing legs 2 Myriapoda. 



Six thoracic legs : No abdominal legs 5 Insecta*. 



Mr. MacLeay, on whose system I shall now say a few 

 words, divides his sub-kingdom Annulosa into five classes, 

 namely, Crustacea, Ametabola, Mandibulata, Haustellata, 

 Arachnida. From the Crustacea he goes by the genus 



* Leach in Entomologists Useful Compendium, by Samouelle, 75. 

 c 2 



