492 



ZOOLOGY 



SECT. 



390 lit, and Fig. 391, h), a narrow tube contained in the pericardia! 

 sinus. It is pierced laterally by several pairs of apertures or ostia, 

 provided with valves opening inwards, and is continued in front 

 into a narrow tube, the cephalic artery (c. art.), which extends into 

 the head and gives off near its origin a pair of arteries to the shell- 

 glands. When the heart contracts, the blood is driven through 

 these arteries to the head and carapace : it then travels backwards 

 in the intestinal sinus, passes to the limbs, and is returned to the 

 pericardia! sinus, finally re-entering the heart, during its diastole, 

 through the ostia. The plasma of the blood is coloured red by 

 hemoglobin, and contains amoeboid corpuscles. 



As already mentioned, the function of respiration is discharged 

 by the flabella and bracts of the feet, which are abundantly sup- 



FIG. 301. Transverse section of Apus. cm. muscles to feet ; dv. dorso-ventral muscles ; e. eggs ; 

 tl'iii. dorsal muscles ; g. ovary; di: dorso-ventral muscles ; li. heart ; i. intestine ; m. partition 

 between intestinal and lateral sinus ; vm. ventral muscles. (From Bernard.) 



plied with blood, and the movements of which ensure a constant 

 renewal of the water in their neighbourhood. The. renal organ 

 or shell-gland (Fig. 392) consists of a coiled urinary tube (uc.) 

 lying between the two layers of the carapace and lined by gland- 

 cells. At one end the tube is connected with an e^id-sac (ts.\ 

 also lined with glandular epithelium ; at the other it dilates into 

 a small bladder (b.) which opens on the second maxilla (m.). 



The nervous system (Fig. 393) is constructed on the annulate 

 type. There is a squarish brain (br.) situated in the dorsal region 

 of the head, beneath the eyes. From it a pair of cesophageal 

 connectives pass backwards and downwards to join the ventral nerve- 

 cord, which consists of a double chain of ganglia (gn. 1-4) united 

 by longitudinal connectives and transverse commissures so as to 

 have a ladder-like appearance. The first pair of ganglia lies 



