DEFINITION OF THE TERM INSECT. 19 
to disappear in the Pupipara Latr., or the genus Hippo- 
bosca 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 tracheze, that some 
have a heart and circulation and others not, that some 
have double sexual organs and some single, 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 Myriapoda. 
Sub-kingdom Awnnuxata Cuy. 
* Gills for respiration. Classes. 
Legs sixteen: .... Antenne two or four............ 1 Crustacea. 
** Sacs for respiration. 
Legs twelve : ..... ANtenma NONEC.........00sseeerese 3 ARACHNOIDEA, 
*** Tracheze for respiration. 
a. No Antenne. 
ee Sees peice ee verleldadewaishieisn's celenivenansoeds snes suse 4 Acari. 
b. Two Antenne. 
Six thoracic legs: ... Abdomen also bearing legs... 2 Myriaropa. 
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 Entomologist’s Useful Compendium, by Samouelle, 75. 
c2 
