58 Papers from the Department of Marine Biology. 



As can be seen from figure 10, the ovary invades the abdomen to a 

 great extent. The great size of the abdomen is perhaps best appre- 

 ciated in a side view (fig. 9). 



By the time that Stage VII has been reached the gall is almost closed. 

 Fertilisation takes place when this stage is reached (see next section). 

 After closure of the gall the male is unable to pay further visits, so 

 fertilisation must be confined to a brief period and may occur only once. 

 But the spermatozoa must retain their vitality for a long time within 

 the spermathecae, for oviposition proceeds until the gall crab dies, and 

 a large number of successive broods are probably produced. 



THE MALE. 



I have mentioned above the fact that the male of Hapalocarcinus 

 has remained unknown up till the present, and have quoted Caiman's 

 conjecture that the sexes both become mature during a free-living 

 phase and that after impregnation the female settles down and forms 

 a gall in which she is imprisoned. I was myself at first inclined to 

 believe that in Hapalocarcinus we had another example of protandric 

 hermaphroditism, like Lysmata seticaudata, described by Spitschakoff.* 

 This seemed to be indicated by the male-like appearance of the young- 

 est inhabitants of galls with their narrow abdomens. But the absence 

 of male apertures and copulatory styles supported the alternative sup- 

 position that they were immature females. For some time, then, I 

 was unable to find an undoubted male, though I examined as many as 

 a hundred galls. But at length, on examining one which was just 

 closing, I found it occupied by a female (Stage VI) with her recently 

 moulted skin and a much smaller individual of about 1 mm. carapace 

 length. This was identified as a male on account of the well-developed 

 and typical copulatory styles and a pair of enormous testes full of 

 mature spermatozoa, which appeared as opaque white structures in 

 the cephalothorax. From this discovery, which I confess was never 

 repeated, I conclude that the male is normally very much smaller than 

 the adult female and not even so large as the young immature females 

 which are found in the least-developed galls; also that he is free-living 

 and visits the females within the galls, copulation taking place at a 

 period when the gall is still open, but the ovary of the female is already 

 well grown. As in the other Brachyura, so here it only occurs just after 

 the female has moulted. Soon after a stock of sperm has thus been 

 secured the gall closes up, so that the visits of other males are barred. 

 But the female begins to lay eggs and lays apparently brood after 

 brood, which develop within the ample shelter of the abdomen until 

 they reach the zoaea stage. Then the larvae are liberated to the exterior 

 through the tiny circular outlets of the gall. 



*Zeit . wiss. Zool., Bd. 100, p. 190, 1912. 



