32 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



third pair has a foliaceous outer ramus in the female, and a 

 much larger styliform one in the male. In this species, there is 

 great difference between the male and the female in the length of 

 a long styliform process extending backwards from the mid-dor- 

 sal line of the third abdominal segment. 



The secondary sexual characters are not acquired completely 

 until maturity is reached. The female form may be looked upon 

 as the more primitive, for the young, when first escaped from the 

 egg, generally resemble the female rather than the male. In 

 examining a large number of specimens of Orchestia agilis from 

 Woods Hole it was found that all individuals up to about 7 mm. 

 in length have gnathopods like the female, and in two or three 

 individuals about 7.5 mm. long the first gnathopods were of the 

 male form, and the second pair, of the female. The gnathopods 

 were of exactly the same form as those of the respective adult 

 forms and showed no sign of transition between the two. 

 Although it has been known that the male characters are acquired 

 gradually, there have been no accounts of the condition in which 

 one pair of appendages is male and another female. 



SIZE. 



The Amphipoda of Connecticut are in general of small size. 

 The largest species of the coast is probably Gammarus locust a 

 a few specimens of which, collected at New Haven, had a length 

 of 30 mm. As in many other groups of animals a larger size is 

 attained in the Arctic regions or in the cold waters of great 

 depths. Thus Sars records a length of 48 mm. for Gammarus 

 locusta in the Arctic regions, and Professor S. I. Smith (Ann. 

 and Mag. Nat. Hist., ser. 5, vol. 14, page 181, 1884) records an 

 Amphipod, Eurysthenes gryllus Boeck, dredged by the "Alba- 

 tross " in 1917 fathoms which had a length of 4^/2 inches. This 

 probably represents the largest known member of the group. At 

 the other extreme of size are Stenothoe, 2 mm., Dexamine thea, 

 3 mm., and Corophium cylindricum, 3-4 mm. in length. 



COLOR. 



The colors of the Amphipoda are frequently quite brilliant in 

 life, but with scarcely an exception specimens bleach to such an 



