NEPHROPS. 221 



|P The testes are a pair of organs lying in the dorsal part 



of the thorax. They lead by paired tubes, the vasa 



deferentia^ continuous with the testicular cavity, 



* to the exterior on the last leg. The ovaries are 



also paired, and in a similar way lead to the exterior by paired 



tubes, the oviducts^ on the anti-penultimate leg. 



The eggs are shed in great numbers and adhere to the 

 swimmerets of the female. In this condition the female 

 is known as a " berried " lobster, and swimming is at that 

 time impracticable. The male discharges the male element 

 upon the eggs and development takes place within the egg- 

 membrane. 



The full development of the Norway lobster has not 

 been followed, but its close ally the crayfish has been well 

 studied. 



The chief points of special importance in the develop- 

 ment are as follows : — f 



1. The egg has a large amount of yolk arranged 

 symmetrically and the segmentation is equal and super- 

 ficial. (See page 49.) 



2. Invagination takes place at one spot, resulting in a 

 sac of endoderm pushing into the yolk, the blastopore 

 closing. 



3. The endoderm cells ingest the yolk within themselves 

 and thus come to lie close under the ectoderm. 



4. From the middle line (future ventral surface) 

 the ectoderm invaginates to form stomodseum and procto- 

 daeum, which open into the archenteron and form the 

 gullet and stomach and the intestine respectively. 



5. Paired thickenings of the ventral surface form the 

 head, the thorax and abdomen and the paired appendages. 



6. The first three pairs of appendages to appear are the 

 antennules, antennae and mandibles, the embryo at this 

 stage being somewhat comparable to the nauplius larva of 

 some other Crustacea. (See page 242.) 



7. The paired appendages then appear gradually in 

 order backwards and the young crayfish hatches, with a 

 cephalothorax distended dorsally with yolk. 



[Table. 



