Habits of' the Limnoria Terebrans. 319 



narrower than the other segments ; the fifth is the broadest, the 

 second, third, fourth, and fifth, are nearly equal in length. The 

 succeeding six are considerably shorter, while the two fornjing 

 the last divisions of the tail are the longest of the whole. The 

 head is nearly spherical in form, and bears four antennae, two 

 eyes, and the organs of the mouth. Each of the seven succeed- 

 ing segments is provided with a pair of articulated feet, and four 

 of them with scales on the ventral surface, forming a kind of 

 sac, in which the young are carried for some time after their ex- 

 clusion from the egg^ The segments of the tail bear, ventrally, 

 six pairs of scale-like appendages, arranged in three rows, and 

 two pairs of styles, one pair projecting on either side from un- 

 der the terminal edge of the last segment. The whole of the 

 dorsal surface is covered with stiflp pinnated hairs, longer than 

 those of other small Crustacea. Amongst these hairs numerous 

 minute parasites, somewhat like Echinorynchi and Acari, are 

 constantly to be seen. They even infest the branchiae. 



II. Anatomical Details, 



In so far as the structure of the Limnoria agrees with tb£^t of 

 other and well-known crustaceous animals, I shall not describe it 

 minutely ; the chief object of such memoirs as the present being, 

 as I conceive, to point out those peculiarities which distinguish a 

 particular species from its congeners, and fit it for the purposes 

 it is destined to fulfil. With regard, therefore, to the organs of 

 support, — the frame-work of the organization which is to en- 

 gage our attention, — I need only remark, that, in their constitu- 

 tion and arrangement, they are the same as those of allied animals. 

 The crust covering the segments of the body and of the tail is 

 rather soft, but distinctly calcareous. It is harder, and even 

 brittle on the head. It effervesces with acids, but not strongly. 

 It is translucent in the fresh state, so as to admit of the motions 

 of the legs being seen through the body, as well as the general 

 arrangement of the viscera. The ligaments connecting the seg- 

 ments are somewhat more brittle than those in similar animals. 



The organs of motion are the fourteen legs, the tail, and 

 certain subcaudal appendages. These last are used in swim- 

 ming, but ought to be regarded chiefly as organs of respiration. 



