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Part III. — Twenty -second Annual Report 



The endopodite and exopodite of the pleopod are very different from 

 one another, and their different functions are very evident from a minute 

 examination of their forms. They will therefore be described below in 

 detail. 



In addition to the discussion of this question in the case of Cancer 

 pagurus, observations on the spawning of Carcinus mcenas, and on the 

 manner of egg-attachment in Homarus, Nephrops, Munida, and other 

 forms, will be added. 



The Swimmerets. 



There are four pairs of swimmerets, attached to the second, third, 

 fourth, and fifth abdominal joints respectively, fig. 15. Each consists of 

 an outer, the exopodite (ex.), and an inner branch, the endopodite (en.). 



The description of the swimmeret of Carcinus mamas by M'Intosh* 

 applies very well to Cancer pagurus : — "First pair of Abdominal Feet. — The 

 internal limb [endopodite] is clothed for the most part with long, delicate, 

 silky hairs, which are simple throughout, with the exception of some 

 branched hairs at the base, best seen on the anterior surface of the fore- 

 most limb. The former are pale and translucent, and come off in distinct 

 bundles all the way up from their commencement. The tufts above the 

 middle joint arise from the upper part of each of the pseudo-joints that 

 compose the flabellar extremity, being situated, likewise, only on the 

 posterior surface and sides of the limb, the anterior surface being free. 

 The hairs themselves are very beautiful, presenting externally a brownish 

 or yellow outline, within this a pale streak, and then a more or less 

 granular central portion . . . The external limb is covered with 

 branched hairs from base to apex along both outer and inner edges, the 

 hairs on the outer row being rather longer than those on the inner. A 

 few short, smooth bristles are distributed over the general surface of the 

 limb." " The ova, when present, are attached solely to the inner limb of 

 each abdominal appendage." 



The Endopodite. 



The endopodite (Cancer pagurus) is long, cylindrical, tapering to a blunt 

 point ; it is bent slightly in bow-shape, the concavity being towards the 

 anterior side. Over its whole length it bears tranverse rows of long, 

 stiff, slender hairs. These rows are not set at right angles to the long 

 axis of the endopodite, but run obliquely downwards from the inner 

 (next the median line of the abdomen) to the outer edge, en., fig. 20a. 

 They are moreover confined to the posterior surface, their ends appearing 

 at the edges only of the anterior surface. On the outer edge they come a 

 little further on to the anterior surface than on the inner side, en., fig. 

 20b, and fig. 63, which gives a plan of one of the rows. The tips of the 

 two endopodites of opposite sides meet in the middle line, and the hairs 

 on their inner surfaces are together bent forwards, fig. 13. The hairs 

 are thus pointed in every direction. The arrangement of the hairs on 

 the posterior surface of the tip is shown in fig. 62. 



The hairs from their extreme thinness are very flexible. They are 

 perfectly smooth, except near the tip. The latter ends in a sharp process, 

 and close to the extremity of the hair there are a number of delicate 

 cilia (fig. 23a). The tips of the hairs do not all conform to this type. 

 Considerable diversity of structure was found in different hairs, vid. figs. 

 22, 23, 31, 33 ; they usually, however, end in a more or less acute 

 point, and the cilia are generally to be made out. It is probable 



* M'Intosh, "On the Hairs of Carcinus mcenas." Trans. Linn. Son/., vol. xxiv., p. 97. 



