ON THE BRITISH EDRIOPHTHALMA. 4t 



in different deprrees of strength, to the margins of the limbs generally (PI. 

 XVir. fig. Al). 



2nd. Are longer in general form, and are fringed on one side with a 

 series of fine, straijiht teeth-like processes, assuming a rake-like character. 

 These are attached to the maxilliped, as also another variety (PI. XVII. fig. 

 A 2). 



3rd, Differs from the last in having the teeth bent in a curve directed 

 to the base (fig. A 3). 



4th. On the carpus of the second gnathopod (the second thoracic foot 

 of authors), the hairs are two very distinct varieties, which appear to 

 originate from closely approximating bases. One is long and slender, naked 

 until the extreme point, where appear a few exquisitely delicate cilia, which 

 give to the extremity a bulbous appearance, which can be resolved only 

 with a 700 magnifying power (fig. A 4). 



5th. Tiie other is short, broad and flat, terminating in a point which is 

 sharply turned upon itself; the margins of the hair are likewise furnished 

 with a series of minute teeth pointing towards the base, ranged on each side 

 for about two-thirds of the entire length of the hair (fig. A 5). 



6th. Again, upon the same member on the propodos, we find two other 

 forms, though decidedly moulded upon the type of the two preceding. The 

 shorter form loses the hook-like point in a bulbous termination, and the 

 shaft is furnished with teeth but on one edge (fig. A 6). 



7th. On the appendage to the mandible a variety of this last form exists 

 (fig. A 7). 



8th. Represents the longer variety, and shows a decided increase of 

 strength ; it is slightly turned at the extremity (fig. A 8). 



9th. These hairs are situated on the first gnathopod, and assimilate to 

 No. 6 on the second in general form, but are minus the serrated margin; 

 on one side of the extremity is a fine hair (fig. A 9). 



10th, 1 1 th, 12th are varieties of the plumose form, and are chiefly found upon 

 the second antenna, though a few are present at several parts of the animal 

 besides. Besides these, there are numerous modifications of a less distinct 

 form of many of them in different positions of the animal (fig. A 10, 11, 12). 



To become acquainted with the whole, so as to make the knowledge avail- 

 able to any practical result in the determination of species, would partake of 

 too exclusive a study, and one that would not be commensurate to the labour 

 entailed, if the great variety of forms were generally constant. It is not 

 often that we meet with this obstruction. 



On Talitrus locusta (the common shore sand-hopper). — There appears to 

 be but a single kind of hair with but little modification of form to meet the 

 conditions of distinct parts. They are short, stiff", blunt spines, and exhibit 

 under the microscope a tendency to a spiral condition for about one-fourth 

 the length of the whole from the extremity, at which distance a second, but 

 smaller process, exists, so that the hair might be characterized as forked, but 

 that the great inequality of the two terminations would scarcely admit the 

 idea to be realized (PI. XVII. fig. B). This kind of termination to the hair 

 is by no means rare in the order. Those found in Gammarus are scarcely 

 more than modifications of the same form, and not very important in their 

 change, a circumstance which lessens the confidence in the expression of 

 any opinion obtained from their observation. 



But still the close examination of the hairs taken from positions homolo- 

 gically the same in different species, may not unfrequently be found an 

 auxiliary of greater or less importance in the study of closely-allied species. 



The process of moulting, — The Amphipoda, as all other Crustacea, renew 



