"tary J, 



[Prom the American Journal op Science and Arts, Vol. VII, June, 1874.1 



Tube-building Amphipoda ; by S. I. Smith. — In examining 

 recently an alcoholic specimen of a species of Xenoclea, I no- 

 ticed a peculiar opaque glandular structure fdling a large portion 

 of the third and fourth pairs of thoracic legs, which in most, if 

 not all, the non-tube-building Amphipoda are wholly occupied by 

 muscles. A further examination shows that the terminal segment 

 (dactylus) in these legs is not acute and claw-like, but truncated at 

 the tip and apparently tubular. In this species, a large cylindrical 

 portion of the gland lies along each side of the long basal segment, 

 and these two portions uniting at the distal end pass through the 

 ischial and along the posterior side of the meral and carpal seg- 

 ments and doubtless connect with the tubular dactylus. There 

 can be no doubt that these are the glands which secrete the cement 

 with which the tubes are built, and that these two pairs of legs 

 are specialized for that purpose. 



A hasty examination revealed a similar structure of the corre- 

 sponding legs in Amphithoe macidata, Ptilocheirus pingicis, Cera- 

 pus rubricomis, Byblls Gaimardi, and a species of Ampelisca. 

 In all these except the last two a very large proportion of the 

 gland is in the basal segment. In the Amphithoe this segment is 

 thickened and the gland is in the middle. In the Gerapus it is 

 very broad and almost entirely rilled by the gland, with only very 

 slender muscles through the middle, and the orifice in the dactylus 

 is not at the very tip but sub-terminal on the posterior side. In 

 the Ptilocheirus the gland forms three longitudinal masses in the 

 basal segment and is also largely developed in the meral and car- 

 pal segments. The dactylus is long and slender and the orifice 

 sub-terminal. In Ampelisca and Byblis (which, like Maploops, 

 are tube-building genera) the meral segments of the specialized 

 legs are nearly as large as the basal and contain a proportionally 

 large part of the gland. In these genera the remarkable elonga- 

 tion of the two distal segments in the third and fourth pairs of 

 legs is perhaps a special adaptation to enable them to reach back 

 over the deep epimera. 



The examination of fresh specimens will doubtless show these 

 structures much more fully. 



6 



