102 



Part III. — Twenty -third Annual Report 



During the examination of the ovaries of the lobster no case was found 

 in which the eggs showed a perivitelline space when in the ovary. Large 

 ovarian eggs, however, as a rule, develop a perivitelline space if left some 

 time in sea-water. A lobster that cast on July 9th 1904 died five days 

 later. The ovarian eggs measured 1*75 x 1*4: 1*7: 1*65 x 1*4: l'5mm. 

 The eggs were teazed out in sea- water and two or three hours afterwards 

 showed considerable perivitelline spaces. The space usually shows more 

 on one side than on the other ; it is clear and colourless. 



A lobster that hatched its eggs in the summer of 1904 and cast 

 immediately afterwards was dead on October 23rd 1904. Some ovarian 

 eggs were separated and put into sea-water. An hour afterwards the 

 eggs, in most cases, showed a more-or less well-marked perivitelline space. 

 Next morning the eggs kept in the sea-water overnight had very large 

 perivitelline spaces. The eggs were yellow- -dead. 



The egg of the lobster has two envelopes : — (1) Outside — the chorion. 

 (2) Within the chorion, and closely applied to the egg — the vitelline 

 membrane. This envelope is well seen sometimes when a perivitelline 

 space has been developed in sea-water. 



The External Eggs. 



When the eggs are just spawned they are of a deep greenish black 

 in colour, with a little clear area at one pole. As development proceeds, 

 the clear area becomes pink in colour, and by the month of October in 

 some lobsters the future limbs and the black pigmented eyes were already 

 made out. The transparent pink area steadily grows larger at the 

 expense of the black yolk, until, when the eggs are nearly ready to hatch, 

 the black yolk may be reduced to half, or even much less, of the mass of 

 the egg. The black yolk occupies the cephalic and gastric regions in the 

 larva. 



The external ezgs measured on May 17th were of the following 

 dimensions :— 2*2 x 2: 2-15 x 2*1: 2-1 x 2-05: 2-25 x 1*95 : 2-25 x 

 2: 2-15 x 2: 21: 2'1 : 195 x 19: l'95mm. The eggs are, for the 

 most part, oval. They were well developed, the pink area being about 

 one-fifth of the whole mass of the egg. In some of the eggs examined in 

 June the black yolk had disappeared ; most of the eggs showed a large 

 mass of black yolk. 



When ready to hatch, the eggs are of various colours, viz. transparent 

 pink, transparent blue, transparent green, except for the black area 

 which marks the yet unused-up yolk. The largest eggs show the least 

 black area ; in them the black has practically disappeared. The eggs 

 increase greatly in size before hatching, and at that time it is difficult to 

 dissect them off the swimmerets without rupturing the zona radiata. 

 The following measurements of various eggs were made in August 1902; 

 the eggs were, as a rule, distinctly oval in shape : — 



Pink egg,* 2-5mm. ; pink eggs, 2-8 x 1-95: 2'4 x 2*15 : 2'35 x 

 2'25mm. 



Egg, blue and yellow, 2-5 x 2'45 : *3'2 x 2-55: *2'9 x 2-4mm. 

 Egg, deep blue, 2-35 x 2'3mm. 



Egg, red, 2-05 x 1-9: *2«9 x 2-6: *3*15 x 2-8: 2*8 x 2'6mm. 

 In the last egg the heart of the embryo was seen beating. 



The Number of External Eggs. 



Buckland calculated the number of eggs borne by a female. He first 

 counted the number on one foot and from that deduced the total. 

 This was 24,960 eggs. Ehrenbaum found that the larger the 



* Zona ruptured. 



