DECAPODA. 



523 



-1 



as copulatory organs in the Xephropsidae, Galatheidea and 

 the Brachyura, but in the Caridea and Scyllaridae this is never 

 the case. The other abdominal limbs are more or less reduced 

 or absent in the higher Decapoda, though 

 some are generally retained in the female 

 for the support of the eggs and young. 



The nervous system of Decapods is referred 

 to at p. 443, and the sense organs at pp. 328/f 

 and 350. A glimpse into the high psychologi- 

 cal development attained by the Brachyura 

 is afforded by the remarkable habit possessed 

 by many of the Oxyrhyncha of decking them- 

 selves (cf. p. 544) with pieces of seaweeds 

 and colonial animals (such as Alcyonium and 

 Ascidians) among which they live. They 

 thus by their own activity attain a result, 

 that of blending in appearance with their 

 environment, which in Hippolyte varians is 

 attained by a complex reflex action (p. 444). 



The heart is perforated by three pairs of ostia, two dorsal and 

 one ventral. An anterior median artery carries the blood to the 

 brain and eyes, and anterior paired arteries supply the antennae. 

 Paired hepatic arteries ventral in origin supply the stomach, 



FIG. 319. Third ab- 

 dominal limb of Axius 

 acanthus. 1 endopo- 

 dite ; 2 appendix in- 

 terna (" stylamblis "). 

 After Borradaile. . 



FIG. 320. Longitudinal section through Astacus fluviatilis (from Claus, after Huxley). 

 Aa abdominal aorta, the sternal artery (Sta) is given off close to its origin ; Ac cephalic 

 aorta ; C heart ; D intestine ; G brain ; Go genital opening ; Km masticatory stomach ; 

 L liver ; N, ganglionic cord ; Sf lateral plate of the caudal fin ; T testis ; Vd vas deferens. 



liver and gonads, and a median abdominal artery carries the blood 

 to the hind end of the body. The unpaired sternal artery descends 

 vertically, passes through the ganglionic chain and divides into 

 anterior and posterior trunks which run above the sterna of the 



