50 report — 1877. 



Reaumur described exuviation in the Crayfish (Astacus Jluviatllis) as being 

 one of great labour and difficulty, as "well as being of long duration. 



In all the cases that the Reporter has observed in the common Shore- Grab 

 (Carcimis mamas), and they have been numerous, the process has been easily 

 and quietly performed in a short time, when conditions have been favour- 

 able, and without a struggle. One condition is the capability of securing 

 the feet in some crevice or notch ; another is retirement. Unless it 

 has the former, the duration of the period is considerably prolonged ; it 

 seems to be almost impracticable, since without it there would be no 

 point of resistance against which the animal can act in its efforts to with- 

 draw itself from the old structure. Neither of these conditions was pro- 

 bably present in Reaumur's experiment ; hence the animal had the appear- 

 ance of undergoing prolonged labour and struggling. 



One specimen of the Common Crab the Reporter frequently took into his 

 hands, and with a pair of scissors cut away the old carapace as it was 

 loosened and raised from the surface of the new shell. After the whole of 

 the integuments had been removed from the animal, it hung attached to tho 

 cyestalks reversed ; here it continued for a considerable time, nor had the 

 animal power to free itself from it without assistance — a circumstance that 

 induced the Reporter to conclude that the anterior portion can only bo re- 

 moved by the assistance of the legs, which failed in this instance because the 

 carapace being cut away, the legs had no object against which to press. The 

 carapace, therefore, is rejected naturally in an inverse direction, and only 

 returns to its old position by the elasticity of the membranous ligaments that 

 have not been ruptured. 



This has been interestingly exemplified by a scries of Trilobites that have 

 been found in the locality of Newton Abbot, many of which were observed 

 with the heads reversed lying close to the bodies of the animals. There is 

 no doubt, I think, but that all the specimens so found were the exuviations 

 of animals then living rather than the representatives of defunct ones. 



When they have thrown off the old skeleton, the Crustaceous animals are 

 very liable to become the prey of others, both of their own and other forms. 

 Of this they appear to be aware, and are consequently more afraid of an ap- 

 proaching object, and through fear are much more active and less easily 

 caught than at any other period. 



It is at this time also (that is, immediately after shedding the skin) that 

 the female is in a state adapted for the approaches of the male. For some 

 days previously the male may bo seen running about and hiding itself under 

 stones and in crevices of the rocks, holding the female clasped by one or more 

 of its legs, tho carapace of the female being pressed against the sternum of 

 the male. In this position they continue until the female throws off 

 the old calcareous shell, when the female is reverse in its position relative to 

 the male, and connexion between the two immediately ensues, and continues 

 for a day or two, perhaps iintil the shell of the female attains its hard calca- 

 reous character. 



It would therefore seem to be tolerably certain that the period of the 

 exuviation in the male must be at a separate period of the year from that of 

 the female. 



Mr. Gosse, in the ' Annals of Natural History,' 2nd series, 1852, vol. 

 x. p. 210, gave an account of his observations of a crab (Maia sqmnaih) 

 during the period of moulting, in which he appears to confirm all that has 

 been previously described as to the manner in which the Brachyura and Ma- 

 crura get rid of the old integuments. 



