264 



MANUAL OF ELEMENTARY ZOOLOGY 



that the antennules bear on their outer flagella bristles which 

 subserve the sense of smell. Various of the setae, especially 

 those of the antennas, are organs of touch. 



The sexes of the crayfish are separate. The generative 



organs lie in the thorax, above the gut and 



Reproduction. bdow the pericardium They have the same 



general shape in the two sexes, consisting of three lobes, 

 two anterior and one posterior, with a pair of ducts, which 

 start from the junction of the anterior and posterior lobes 

 and run to the limbs on which they open. The ovary is 



Fig. 168. — The reproductive organs of a female crayfish. — 

 After Suckow. 



od., Oviduct ; ov. t ovaries ; oz»\, fused posterior part (median lobe); 

 z/«., female aperture on the second walking leg (/S), 



larger and broader than the testis, and has an internal 

 cavity into which the eggs are shed. The oviducts are 

 short, straight, and wide ; they open upon the coxopodites 

 of the second pair of walking legs. The testes consist of 

 a number of branching ducts which end in small alveoli, 

 in which the spermatozoa are formed. The vasa deferentia 

 are narrow and much coiled ; their first part is very slender 

 and translucent, the second part, which forms most of 

 the duct, is wider and glandular, and a short terminal 

 region has muscular walls which force out the sperm. 

 The spermatozoa are discs with stiff, pointed processes 

 round the edge. Inside the disc is a round capsule and 



