ANATOMY OF AN ARTHROPOD. 



105 



There are no blood-vessels 



slit-like openings along the sides of this organ are called the ostia, 

 through which the blood returns to the heart, to be pumped out 

 afresh to the body through the opening in front by a rhythmical 

 contraction of the walls of the tube, 

 as in higher animals ; the blood is 

 poured into the body cavity, and 

 there bathes the organs and comes 

 in contact with the respiratory tubes. 



An opaque-white mass of fat, the 

 fat-hody, surrounds, or nearly so, the 

 abdomen. 



The digestive organs can be easily 

 unravelled, so that each part is dis- 

 tinctly visible. The alimentary tube 

 is short, and convoluted in the hinder 

 parts. The first portion is lodged 

 in the head, and is called the buccal 

 cavity, into which open two glands, 

 one on each side, the salivary glands 

 (Sg), by a single salivary duct (Sd) 

 in a median aperture. Then follows 

 a narrow gullet or msophagus (Oes), 

 which gives rise to a sack which is 



...,..,., , . n Oes, ffisophagns ; Sd, salivary 



Situated m the thorax and part OI duct ; Sg, salivary glands ; P, 

 ,111 ,1 / T-i\ mi proventriculQS ; G, gizzard ; U. 



the abdomen, the crop (P). ihe - - -'- " 



crop is thin-walled ; but the next 

 division, the gv^eai-d (G) or stomach, 

 has hard muscular walls and con- 

 tains six large teeth. These ali- 

 mentary parts are known as the stomatodteum, being formed 

 by an anterior invagination in the embryo. The stomato- 

 daeum has a chitinous lining continuous with the chitinous 

 cuticle of the head. Following the gizzard will be observed a 

 short thin tube, which forms a connection between the original 

 anterior and posterior invaginations of the embryo. It is called 



. 41. — Digestive Organs of 

 THE Cockroach. 



hepatic cajca : Mc, Malpighiau 

 tubes ; Li, large intestine ; Si, 

 mesenteron ; R, rectum ; M, anal 

 gland ; Gb.g, cerebral ganglia ; S.g, 

 sub - oesopiiageal ganglion ; n.c, 

 nerve - collar ; Th. i to Ah.g 6, 

 ganglia. 



