CH. XII] 



ASTACUS 



195 



FIG. 74. To illustrate the process of " ecdysis " in Arthropoda. 

 A. The anterior portion of the body of a Dragon-fly, Aeschna cyanea freed 

 from the larval shell. B. The tail being extricated. C. The whole 

 body extricated. D. The perfect insect, the wings having acquired 



their full dimensions, resting to dry itself preparatory to the wings being 

 horizontally extended. 



of pellets of shot and are filled with a dark red yolk. These when 

 ripe are shed to the exterior through, the short straight oviduct 

 and become attached to the swimmerets of the abdomen by their 

 adhesive coats, and in this position they are fertilised and accom- 

 plish their development, becoming free from the mother only when 

 they have become little crayfish. 



FIG. 75. 



76. 



FIG. 75. Male reproductive organs of Astacus fluviatilis x about 2. From 

 Howes. 1. Eight anterior lobe of testis. 2. Median posterior lobe 

 of testis. 3. Vas deferens. 4. External opening of vas deferens. 

 5. Eight fourth ambulatory leg in which the vas deferens opens. 



FIG. 76. Female reproductive organs of Astacus fluviatilis x about 2. From 

 Howes. 1. Eight oviduct. The left oviduct is shown partly opened. 

 2. Eight lobe of ovary. 3. Left lobe of ovary with the upper half 



removed to show the cavity of ovary or coelom into which the ripe ova 

 drop. 4. External opening of oviduct. 5. Eight second ambulatory 

 leg on which the oviduct opens. 



From the lining of the testes male germ-cells are formed we 

 say advisedly, male germ-cells not spermatozoa, for these cells are 

 utterly unlike spermatozoa. They are rounded saucer-shaped cells 

 with a central nucleus and a number of curved spines sticking out 

 tangentially from the surface by means of which they adhere to the 



132 



