NEPHROPS. 221 
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 ovéducts, 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 :— 
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 stomodzeum and procto- 
deum, 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, antennz and mandibles, the embryo at this 
stage being somewhat comparable to the zauplius 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. 
Reproductive. 
[ TABLE. 
