220 E. W. SEXTON. 



Norman I have been able to compare it with a Norwegian specimen of 

 tulcrculatus, also a large male, 4 mm. in length, and as a result of this 

 examination, I think there can be no question but that the two species 

 are identical, armatus being the fully-developed animal. 



As I have shown before (35), p. 849, the Amphipoda undergo con- 

 siderable modification, even after reaching sexual maturity, the 

 characters most noticeably affected being : the antennae, the number 

 of the joints in the flagella increasing and the proportions of the 

 peduncle joints altering with growth ; the second gnatliopods, the hand 

 of which increases in size and alters in shape to a far greater degree 

 than the hand of the first gnathopod ; and the chitinous cuticle of the 

 body, spinose processes developing, and growing longer, more acute, and 

 more numerous with age. An example of the development of the pro- 

 cesses of the cuticle, bearing on the present case, will be found in the 

 paper above referred to (p- 870), where the stages of growth in one 

 species were traced ; the cuticle in the very young animal was perfectly 

 smooth, the spinose processes commencing as slight swellings, and 

 developing at maturity into rounded upstanding tubercles, only 

 assuming their characteristic shape with the further development of 

 the animal. 



It will be seen that the distinguishing points given by Norman 

 to differentiate his species from Bruzelius's are precisely those which 

 would be influenced by age and growth. With regard to the first 

 point — the stronger armature of the body — I found on examining the 

 specimen of tuberculatus that the tubercles are of exactly the same 

 number and arranged in exactly the same manner as the spine- 

 processes of armatus, those on the last peraeon-segment and the first 

 two pleon-segments being larger than the others, as Norman noted in 

 armatus. The 1st segment has two, one behind the other; the 2nd 

 segment three, one median in front of the transverse furrow, followed 

 by two side by side ; the remaining peraeon-segments and two first 

 pleon-segments each have a swelling in front of the furrow, with two 

 tubercles side by side behind. This agrees with Bruzelius's descrip- 

 tion ; * he states (p. 11) that the 2nd, 3rd, 4th, and 5th segments- 

 carry three tubercles each, one in front of the other two ; but, except 

 on the 2nd segment, as described above, the anterior tubercle is not 

 distinctly defined. Boeck's account is the same. Sars, however, 



* "TvJirs ofver dess ryggsida gar en intryckniiig, och paryggen biir det tva sma knOlar. 

 Det andra, tredje, fjerde och femte segmentet liafva, liksom det forsta, en tvars ofver 

 ryggen gaende iutryckning, och tre snia knolar, den ena franifor de tva andra. . . . Det 

 sjette och sjunde segmentet, som aro hopvuxna med hvarandra, hafva pa ryggen tva par 

 knolar. Deras epinierer iiro atskilda. De tre forsta abdoniinal-segmenterna iiro korta,, 

 och af dessa biira de tva forsta tva knolar pa ryggen." Bruz. (p. 11). 



