96 ANATOMY OF AN ARTHROPOD. 



tions, as in the lungs of a vertebrate animal. In the former 

 case the air goes as it were to the blood ; in the latter the 

 blood goes to the air. Exspiration takes place by the muscles of 

 the body contracting and so compressing the tracheal tubes ; 

 inspiration by the elastic recoil of the walls of the tubes. 



The Beproductive System consists in the male of testes, vasa 

 deferentia, vesietdce seminales, and ejaculatory duct. Unlike the 

 worm, a single pair of testes only exist, embedded in the fat 

 below the fifth and sixth segments of the abdomen. They can 

 only be seen in a young cockroach. The tubes leading from 

 the testes to the vesicula3 seminales are the vasa deferentia, one 

 on each side. The vesiculse form two tufts of white glands 

 which hold the spermatozoa, and which open into the anterior 

 part of the ejaculatory duct. The female organs consist of 

 ovaries, which are two sets of long tubular organs in the hind end 

 of the abdomen. Each ovary is composed of eight tubules, 

 uniting to form a single oviduct on each side. In each tubule 

 the ova may be seen in diiferent stages of growth. The oviducts 

 unite before opening to the exterior into a single tube. There 

 is also a body called the spermatheca, which opens by a median 

 aperture on the ninth sternum, consisting of two small unequal 

 csBca. Close behind the opening of the spermatheca are two 

 other apertures, those of the coUaterial glands, much branched 

 and convoluted tubular organs. Externally wiU be seen six 

 strong processes definitely arranged on the ventral surface 

 between the vulva and anus, used as aids to deposit the ova 

 ( = female genitalia). The male has a number of hooks and 

 plates forming an external copulatory organ, the equivalent of 

 the female processes, but asymmetrically disposed. 



The Nervous System (fig. 36), which can be exposed by re- 

 moving the fat body and organs, consists of a supra-aesophageal 

 (a) and a suh-cesqphageal ganglion (c) united by commissures, 

 forming an oesophageal "nerve-collar" (b) around the gullet in 

 the head. Eunning down the ventral surface of the thorax 

 and abdomen is the ventral nerve-chord, which is double. This 



