230 ANNULATA. 
vertebrates. Some points of special interest in the subsequent develop- 
ment are the presence of a segment between that of the antennze and 
that of the mandibles, and the presence of abdominal appendages which 
disappear later. These seem to point to the cockroaches having sup- 
pressed a head segment, probably corresponding to that bearing the 
antennze in the lobster, and to their having in a similar way lost a 
number of abdominal appendages. 
The mesoblast is present in the embryo as paired somites containing 
ceelomic cavities, separate from the hemoccele or blood-space, part of 
which forms the heart. In later development, however, the mesoblast 
walls break up to form the muscles, connective tissue, gonads and 
walls of the heart; the cavities of the somites then become continuous 
with the hemoccele. Thus there is no true perivisceral ccelom in the 
cockroach, a condition agreeing with other Arthropoda. 
The young cockroach only differs from the adult by an 
absence of wings, and it grows gradually into the adult, pass- 
ing through periodic ecdyses or shedding of its integument. 
Hence the cockroach is ametabolic, or developing without 
metamorphosis. 
BLATTA. 
SEGMENTS. APPENDAGES. NERVOUS SYSTEM. APERTURES. 
Prostomium Primary 
: brain. 
I | Antenne. Brain. 
wp 2 Mouth 
8 Mandibles. : 
= : 9 hee Subresophageal 
Bikeqd mass. 
4 6 | 1st Leg. Ganglion 1 , 
& 
tat 7 and u " 2 Suga 
a 8 3rd " " 3 
9 : ¥ i 
10 " 5 
ju ‘i 6 ; 
a 12 " 7: 
a} 13 n 8 : 
6 " 
3 a n Gap 
“4 16 Posterior " " 
17 ganglion 9 
18 | Anal cerci. Anas. P 
