BLATTA. 225 
which is the éacénia or blade and the outer the ga/ea or 
hood, and a long jointed exopfodite usually known as the 
maxillary palpb. The second maxille closely resemble the 
first maxillze in structure, but the /adcal palps (or exopodites) 
are smaller and the protopodites are fused across the 
middle line, as noticed above, the two appendages forming 
the /abium. The head is joined by a neck with small 
sclerites to the thorax. The thorax has three segments, 
called the prothorax, the mesothorax and the metathorax. 
These are freely movable. Each has a pair of /egs on the 
ventral surface, hence the cockroach has three pairs of 
legs. Each has a basal piece or coxa, a small ¢vochanter, a 
long femur and tibia, and a six-jointed ¢avsus terminating in 
two claws. On the dorsal surface of the male the mesothorax 
‘bears a pair of leathery wings (sometimes termed ¢dytra), 
and the metathorax carries a pair of membranous wings. 
The abdominal segments, like those of the lobster, are 
movable, and each has a ¢ergon and sternon. ‘There are 
ten abdominal segments. The terga overlap each other, 
and the 7th comfpietely overlaps the small 8th and 9th; 
hence one can only count eight (1 to 7 and 1o). 
The last or roth is notched, and bears laterally a pair of 
many-jointed anal cerc?. Of the nine sterna, the first isa 
mere rudiment and the gth in the male bears a pair of 
small s¢yées. In the female, the 7th is boat-shaped and 
envelopes the sterna behind it which are adapted for sexual 
functions. Hence in the female only seven sterna can be 
made out externally. At the hind end of the body the anus 
opens and below it is the opening of the genital organs. 
There are no excretory pores, but the respiratory organs or 
tracheze open by ten paired apertures, the s#gmata. Two of 
these open laterally between the thoracic segments, and the 
other eight lie between the terga and sterna of each of the 
first eight abdominal segments. Air is inhaled and exhaled 
through these stigmata by a rhythmic lengthening and 
shortening of the segments upon each other (caused by 
tergal and sternal muscles). 
The external features show a marked contrast to those of the 
lobster. The principal differences are (1) the presence of only one pair 
of antennze ; (2) only three pairs of thoracic appendages ; (3) the absence 
of abdominal appendages (except, perhaps, the anal cerci); (4) the 
M. 16 
