240 Phylum Arthropoda 



tioned the experimental crabs are likely to become retarded in growth. 

 That is to say that when they molt they are likely to increase less in 

 size than would be the case in nature. This effect appears to be cumu- 

 lative, crabs molting more than once falling even further behind in size. 

 Large crabs kept in compartment live-wells, though comparatively more 

 cramped than the small crabs kept in the laboratory, show less retarda- 

 tion of growth upon molting. 



SEASONS OF AVAILABILITY 



Megalops are to be found during July and August and crabs in the 

 first three post-larval instars during August and September. By the 

 following spring these same crabs, then i year old, have reached the 

 6th and 7th instars. 



Mating crabs are occasionally found on the tideflats among seaweed. 

 Molting crabs may sometimes be discovered beneath the inverted shells 

 of bivalve molluscs or otherwise hidden at extreme low tide. Crabs on 

 the verge of molting appear to frequent shallow water and are to be 

 found in large numbers buried in the sand in certain localities during the 

 spring of the year. Except for the fact that the species characteristically 

 inhabits sandy or slightly muddy regions and avoids rocky shores, we 

 can give no rules for finding such areas. Crabs ordinarily found are from 

 3 to 15 cm. in carapace width. For larger material the investigator must 

 either depend upon fishermen or else employ traps of his own. 



METHOD OF COLLECTING 



Crabs in the megalops and early post-larval stages may be collected 

 by hand in small numbers on the shore at low tide. The megalops, which 

 are positively phototropic, are frequently found adhering to barnacles 

 and other small objects; occasionally they are found swimming at the 

 surface, sometimes in large numbers. In the latter event they are ex- 

 tremely difficult to capture. 



The early post-larval crabs may also be collected by hand in small 

 numbers at low tide. They are, however, ordinarily found buried in the 

 sand or otherwise hidden from view. When the sand is disturbed they 

 may sometimes be observed digging themselves rapidly in again. Crabs 

 at this stage of development may often be taken in large numbers from 

 the gear of fishermen operating on the ordinary commercial fishing 

 grounds which, in Boundary Bay, B. C, are about 10 to 12 fathoms in 

 depth. 



HANDLING THE MATERIAL 



Young crabs appear to be somewhat hardier than mature crabs and 

 may be handled without extreme care. In all cases, however, it is im- 



