ANATOMY OF AN ARTHROPOD. 107 



parts of the body and its organs, hence blood-vessels are not 

 so necessary as when one definite area only is for respiratory 

 functions, 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 ; inspira- 

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



The Reproductive System consists in the male of testes, vasa 

 deferentia, vesiculce 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 iu a young cockroach. The tubes leading from 

 the testes to the vesiculee 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 different stages of growth. The oviducts 

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

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

 aperture on the ninth sternum, consisting of two small unequal 

 caeca. Close behind the opening of the spermatheoa are two 

 other apertures, those of the collaterial glands, much branched 

 and convoluted tubular organs. Externally will 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. 43), which can be exposed by re- 

 moving the fat-body and organs. Consists of a supra-oesophageal 

 (a) and a sub-ossojihar/eal ganglion (c) united by commissures, 

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



