■PHYSIOLOGY OF THE INVERTEBRATA. 445 



As a type of the Macroura,.yfe describe in detail the genital 

 organs of Astacus. The sexes are distinct ; and in external 

 form the testis and ovary have each the outline of a gland 

 composed of three lobes (Fig. yy). They also occupy a similar 

 position in the body — viz., behind the stomach and below the 

 heart. There are two vasa deferentia which are united, one 

 on each side of the junction of the three lobes of the testis. 



Fig. 77.— Reproductive Okgans of Astacus. 

 a = testis or spermarium. b = vas deferens, c = coxopodite of fourth 

 ambulatory limb, d = cells of vas. deferens which secrete the sper- 

 matophores. e = ovary. / = oviduct. §■ = coxopodite of second 

 ambulatory limb. 



These ducts are long and coiled, and terminate in apertures, 

 situated on the coxopodites of the fourth pair of ambulatory 

 limbs.* Each lobe of the testis is composed of small ceeca in 

 which the spermatozoa (see Fig. y6, e) are developed. The 

 spermatozoa are united into masses, which become invested 

 by a fine membrane secreted by the cells of the vasa deferentia 

 (Fig. yy, d) ; thus forming the spermatophores. The ovary 

 is composed of three large ceeca, and the ova are developed in 

 this organ. The oviducts are short tubes, which open on the 

 coxopodites of the second pair of ambulatory limbs. The 

 internal walls of the ovary are lined with epithelial, nucleated 



* In the land crabs the male genital aperture is situated on the last seg- 

 ment of the body. 



