524 



CRUSTACEA MALACOSTRACA. 



segments (Fig. 320, Sta). From the arterial capillaries the blood 

 collects into sinuses at the bases of the gills, and after its oxi- 

 dization, returns by branchial veins to the pericardial sinus. 



Alimentary Canal. The masticatory stomach is large and 

 complex in Decapods. The many-lobed digestive gland of the 

 adult is derived from three pairs of simple diverticula in the 

 larva, and, with the pyloric stomach into which it opens, 

 represents the larval hypoblast. 



Excretory Organs. The antennal glands consist of a glandular 

 sac (sacculus} which communicates with the external opening 

 at the base of the second antenna by a contorted glandular duct, 

 usually dilated before its termination into a receptaculum. The 

 sacculus has been interpreted as homologous with the end-sac 

 of the nephridiumof Peripatus (see p. 542). The parts present 

 great variation in different groups. 



In Astacus the apparatus is disposed in 

 two oval masses lying one above the other ; 

 dorsally is placed the receptacle, opening in 

 front on the 2nd antenna, and ventrally the 

 glandular mass, of complex structi4re, and con- 

 taining the sac- 

 c ulus (yellow) 

 embedded in its 

 upper portion. 

 The duct after 

 leaving the sac- 

 culus expands 

 into a complex 

 network of tubes 

 (labyrinth), with 

 green granules 

 in the cells, 

 which forms a 

 cortical layer 

 over the lower 

 surface of the 

 organ. The 

 labyrinth opens 



into a tangled tube occupying the inner (white) portion of the organ, and 

 opening posteriorly into the receptaculum. 



The receptaculum is rarely as simple as in Astacus, but sends 

 out diverticula, which may unite, as in Pagurus Bernhardus 

 into a median tube, extending back as far as the last quarter of 

 the abdomen. 



Reproductive organs. The arrangement of the gonads and 

 their ducts is shown in Fig. 321. The spermatozoa of Decapods 



FIG. 321. Generative organs of Astacus (after Claus). a female, b 

 male. Od oviduct ; Oe genital openings of the basal joint of the 

 fifth pair of ambulatory legs (Fv) ; Ov ovaries ; T testis ; Va 

 vulva on the basal joint of the third pair of ambulatory legs (F" r ) ; 

 Vd vas deferens. 



