122 



Part III. — Ttventy- second Anniuil Report 



TABLE I. 

 CRABS THAT CAST IN' THE MARINE LABORATORY, BAY OF NIGG, 



* Measured several days after casting. 



As was previously* shown, the ratio of increase at each cast varies 

 greatly. In the Table then given the ratio varied from ^ to i. In the 

 present case, in only one instance was the ratio greater than 5, and it was 

 as small as ^. 



The histological changes that accompany the ecdysis of the crab have 

 been dealt with by "Witten. 



At the time when the crab casts, the shell of the three proximal joints 

 of the chela becomes absorbed along certain lines, thereby allowing of 

 the expansion of these joints to permit the withdrawal of the large claw. 

 In fig. 100, Plate IV., is shown the cast chela. The absorption-lines 

 are on the coxopodite, basi-ischiopodite, and meropodite, viz., ah$. The 

 part of the shell lying between the lines is movable. Similar absorption 

 areas appear in the lobster (Herrick). 



0. Distribution. — In discussing the question of the distribution of the 

 crab, I was of the opinion that a group of crabs measuring from 2| to 4 

 inches would be found to inhabit the shore waters just outside lo-w-water 

 mark. This group was distinct from the beach group, which is consider- 

 ably smaller, viz. from i to 2| inches, and is itself smaller than the adult 

 group, which measures from about 4 inches upward ; it is required to fill 

 up the very considerable gap which separates these two groups. ( Vide 

 PL III.) * 



* "Contributions to the Life History of Cancer jxigunis." 



