Hapalocarcinus, the Gall-forming Crab, etc. 



57 



closest embrace and makes its way very slowly over the surface in 

 search of a hole. The legs, though rather weak, are provided with 

 sharp claws which it sticks into the ccenosarc of the colony. If several 

 crabs are contained in the same vessel they come together and fight vig- 

 orously (though under natural conditions they can have no opportunity 

 of satisfying these proclivities). It is clear that the crab is strongly 

 thigmotropic, a property developed in correlation with its secluded life. 



It is first my intention to give an explanatory description of the 

 series of females which are illustrated here. As was stated in the 

 preliminary description, the crab settles down when it is immature. 

 The youngest females, found in galls consisting solely of the chamber 

 A, have a carapace length of 1.5 to 1.75 mm. and their sex is hardly 

 recognisable. They have a narrow abdomen with no trace of swim- 

 merets; there are no reproductive apertures and the genital gland has 

 not developed. But there is equally no sign of male characters and a 

 perfect gradation exists between these apparently sexless forms and the 

 adult female. This youngest female I denote as Stage I. 



In Stage II, though the abdomen is very little broader, rudiments of 

 the swimmerets appear and also the female apertures on the sternum 

 opposite the third thoracic legs. The carapace length is 2.0 mm. 



In Stage III the abdomen is definitely broader, though only in seg- 

 ments 4, 5, and 6. The rudiments of the appendages are rather 

 longer and the first pair show indications of bifurcation. The carapace 

 length is 2.5 mm. 



In Stage IV all the abdominal segments except the last have shared 

 in the increase of breadth. The carapace length is 3 mm. 



Stage V shows further broadening of the abdomen. The carapace 

 length is 3.2 mm. 



In Stage VI the abdomen is almost as broad as the carapace. It 

 will be seen that the hypertrophy is due to the growth of the last three 

 segments. The ovary is well developed in the cephalothorax. The 

 carapace length in the specimens figured is 3.5 mm. This appears to 

 be the same stage as that described and figured by Caiman (1. c., pi. 3, 

 figs. 29, 30), but he gives the carapace length as 2.6 mm., which is very 

 much smaller than that in mine. 



In Stage VII the abdomen is wider than the carapace, the last three 

 segments being greatly widened to form a pouch. In nearly all these, 

 eggs are found attached to the appendages. The two stages figured 

 here show that marked growth takes place even after reproduction 

 commences. This may be estimated from the following figures: 



