228 



ANNO LATA. 



ing it. On contraction of the heart the blood is driven 

 forwards along the dorsal aorta, which terminates near 

 the brain in a funnel opening into the body-cavity. The 

 body-cavity is, therefore, a blood-space or haemocoele in 

 which the blood bathes all the tissues and eventually finds 

 its way back to the heart. Immediately under the heart 

 the pericardial septum stretches across the body cavity, 

 partially dividing it into a dorsal pericardial sinus and a 

 ventral main cavity. The septum is a fenestrated mem- 

 brane^ being perforated by numerous apertures. 



Fig. 151. — Transverse Section of Blatta. 

 (Semi-diagrammatic. ) 



Dorsal Branch of 

 Trachea. 

 Tergon. 



Heart. 



Dorsal Muscles. 



Alary Muscles. 

 Pericardial 

 Septum. 



Stigma. 



Sternon. 



Ventral 

 Muscles. 



Dorso- 

 ventral Muscle. 

 """-^ Gizzard with 

 Teeth. 



^ Hepatic Caeca. 

 Nerve-cordi Body-cavity (a blood-space). 



Passing through the anterior portion of the abdomen. 



The brain lies in the head dorsal to the oesophagus. It 

 has a paired anterior lobe which supplies the 

 eyes and a posterior giving nerves to the an- 

 tennae. A ring round the oesophagus is completed by a sub- 

 oesophageal mass, composed of three pairs of fused ganglia, 

 belonging to the mandibular, maxillary and labial segments. 

 This is followed by a double ventral nerve-chain with three 

 thoracic ganglia and six abdominal. 



The cockroach has a nervous system much like that of the lobster. 

 As in the latter, we can recognise certain fusions. If we start with a 

 brain and a chain with ganglia to each segment we get a total of 

 five cephalic (of which the second has no appendages), three thoracic 

 and ten abdominal ganglia, or eighteen in all. These are reduced to 

 ten by the fusion of the first two to the brain, the fusion of the next 



