High and low Dimorphism. 



3t7 



active part in tlie breedìng season? The explanation of their occur- 



rence is given by examiuing the males that occur during the wiuter 



months, wheu reproduction is not going ou. We find at that season 



a few high males, presumably left over from the passed summer, 



but instead of any low males we bave an assemblage of crabs 



measuring from 5 — 19 mm. 



carapace leugth, ali ofwhich 



exhibit the fiat type of chela 



and reduced testes. What 



bappens is this: the low 



males before they can take 



part again in the breedìng 



season bave to pass through 



a period of active growth 



in wbich the sexual functions 



are suppressed, in order to 



attain to thecoudition of high 



males. This period of growth and sexual suppression is generally 



passed through in the winter, but this is not necessarily the case, 



and so we bave tbe pbenomenon of the middle males with fiat 



Fig. 6. 



Fig. 7. 



chelae and nonfunctional testes occurring in the breeding season, 

 while the breeding males are dififerentiated into high and low forms. 

 B. Inachus thoracicus. This species is closely allied to the fore- 

 goiug, but is clearly dififerentiated in its greater relative length, in 

 tbe larger size of the dorsal tubercles, and by the presence in the 

 male of a large ventral shield. I bave not been able to examine 



