216 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
are joined together end to end in a longitudinal series, the hind 
margin of the anterior slightly overlapping the anterior margin 
of the posterior. Each segment consists of a long dorsal sclerite 
{tergum or tergite) united laterally to a shorter ventral piece 
(sternum or sternite) by a pliable membranous area which pro- 
vides for expansion of the body during breathing. The term 
pleurum or pleuron (plural pleura) is sometimes applied to the 
lateral part of the entire body or of a segment; or pleurite may 
Fio. 3. — Drawing of body of Locust, side view, showing thorax separated from head and 
abdomen, and divided into its three segments. (After Packard.) 
be used for the latter. In the abdomen there is no line of division 
between the pleurite and tergite and the latter term is commonly 
used for both. The entire body of an insect is regarded by 
embryologists as composed of a series of twenty segments (somites, 
metameres) of which six belong to the head, three to the thorax, 
and eleven to the abdomen. In the adult these segments are 
united in various degrees, being quite distinct in the middle of 
the abdomen but unrecognizable in the head. 
Anatomy of a Locust. 
Head. 
In this Locust the head (Fig. 2-5) is ovoid in form, 
somewhat compressed from side to side, placed nearly at right 
angles to the axis of the body, with the mouth on the lower or 
ventral side. The large oval compound eyes are conspicuous 
objects embedded in and projecting from the sides of the upper 
portion (epicranium) . If examined with a compound microscope 
