5i REPORT — 1877. 



simple means to which creative wisdom has had recourse when a natural 

 proceeding was to he regulated. But the most remarkable part of the pro- 

 cess, and that which particularly leads me to present this communication to 

 the Society, is what I found to take place in the larger or claw-legs. 



" In these the flesh of the two outer sections is much shrunk ; but the por- 

 tion occupied by the third, or innermost, is, on the contrary, very much dis- 

 tended. This is especially seen on the inner concave surface of this portion 

 of the limb, where, if we examine the part under ordinary circumstances, wo 

 find three lines, which meet at an angle, their diverging extremities being 

 hounded by a curved border that is directed at its termination towards the 

 body of the animal. As a preparation for exuviation, in the same manner 

 as the well-marked line in front of the carapace or shell between its margin 

 and the mouth becomes loosened by absorption, so this curved line on the 

 claw-leg has become separated along its course, while the other lines (those 

 which are straight and meet at an angle) are only so much changed from a 

 firm crust as still to remain connected together by a membrane, and thus 

 assume the nature and offices of movable joints or hinges. The hitherto firm 

 structure of this part of the claw-leg being thus turned into a movable cover, 

 which admits of being lifted at the curved circumference, the swollen por- 

 tion of the limb is protruded through the opening ; and, by the tension thus 

 produced below, the wasted extremity is drawn downward, the greatest ac- 

 commodation of space being thus afforded with the least expenditure of effort 

 or displacement. 



" In the specimen examined I found that a portion of the muscular sub- 

 stance of the limb had become so much distended as to be thrust out of its 

 sheath, and partly wrapped round the outside of the loosened crust. 



" But while this may be supposed t^o be of great mechanical use in drawing 

 downward the remaining wasted portion of the limb occupying the more dis- 

 tant segments, it offers but a slight hindrance to the final passing of the 

 whole through the final ring or coxa, where the leg is united to the body. 

 For this last remaining space is narrow ; and the distention being chiefly pro- 

 duced by a liquid diffused through the fleshy fibres, it offers but little positive 

 obstruction to the passage. A dragging action, therefore, accompanied pro- 

 bably by a muscular contracting power, is all that is required to enable it to 

 slip through ; at the same time that a portion of the distending fluid, if not 

 the whole, is so much thrust backward as still to occupy the opening, and 

 thus contribute to bring down each successive part in turn. 



" The extremity of the claw-leg, then, being not only smaller naturally, but 

 more wasted in this process than the rest, finds no hindrance to its escape ; 

 and thus the imprisoned limb is set at liberty. It is a fact beyond doubt, as 

 appears by examination of many specimens, that no splitting process takes 

 place in the slender or walking legs. 



" It is a matter of some interest to ascertain whether and to what extent 

 this remarkable process takes place in others of the great family of Crusta- 

 ceous animals ; and I have exercised no small extent of effort in following 

 the examination in species of both the sections, the long-bodied or lobster 

 kind, and the short-tailed or crabs." Mr. Couch's results were not attended 

 with any great success in point of number of species. 



" Nothing of this kind appears," he says, " in the Norwich Crab {Mala 

 sqmnado), C'orj/stes cassivellaunus, the common Crayfish (Palinurus vulgaris), 

 or various species of shrimps. We may therefore conclude that all the limbs 

 in those instances are withdrawn from their covering in the same manner as 



