II.] THE CRAYFISH AND LOBSTER. 21/ 



a. It may be rendered the more obvious by in- 

 flation from the excretory orifice (Sect. B. 4. /.). 



Having inflated in, lay open the basal joint of 

 the antenna ; on entering this, the neck of the sac 

 becomes constricted and duct-Hke. 



2. Tease up a small portion of the glandular segment in 

 eosin solution; examine under a high-power. It is 

 largely composed of a coiled tube, lined by a square- 

 celled epithelium. 



G. The reproductive organs. 



These differ in detail, in the Crayfish and the Lobster. 

 They lie partly ventral to the heart; their general re- 

 lationships have been described (Sects. A. and D.). 

 Dissect the cephalo-thoracic region from the tergal 

 aspect, and remove the heart. Examine the genital 

 apparatus in situ. 



I . The male organs. 



a. The testis. A median greyish-white mass, bilobed 

 anteriorly. 



b. The two vasa defere?itia, arising where the posterior 

 lobe of the testis meets the two anterior. Each is 

 narrow near the gland ; its calibre increases as it 

 proceeds back from it, and, becoming extremely 

 convoluted, it finally ends at tlie genital opening on 

 its own side (Sect. A. c. y). 



These ducts generally contain a dense milk-white 

 product, secreted by their glandular lining (s/>er- 

 viatophoral glands). (Cf. Sect. L. \. h.) 



In the Lobster, the testes are two long tubes which 

 extend back into the abdomen. Their posterior 

 portions meet in the middle line, but in front they 



