. .i n \.-i v 



fKI'STACEA. 



Ckrapac* at OmiMH mmtmi (Outar mmat. Linn.) 



a, , Rri<m of the lomaeh, or fastric reirion ; i, (renital region ; r. cardiac 

 <, poatattor cardiac refion ; . , branchial rrfioni ; /, /, hepatic region. 



Cwapae* of eoBBoa Crawftih (Ailaciu JlunmtUu). 



m, OaaUk rack* ; , fmltal refion ; e, cardiac rrfion ; d, poalcrior cardiac 

 (to.; . . kruckhU Rfflau. 



Uiu rule u reverted, the abdomen being comparative])- small, and the 

 gnat development taking place in the carapace, illustrating the " lui 

 3UJoormit..rKmniquc" of If ~ 



I organiaue" of M. Geoffroy St Hilair*. The Common 

 Crab and Common Lobster afford striking examples of this law of 

 Ofpank equivalent*. 



Ykr af tte aaaVr aid* of I 



..,.,. atonal pt 

 I of IW 



n.; ; .l.M/W, with the tall or 



ro-.tenul pifcn ; *. *, eiteriul 

 ; /,/./.. 

 oa* of la 



tnm law iMaaiai ; UM palp marked saniM la* on dnrtaf iucabatloa. 



View of the under aide of the male of TMflaaa Jlurialilu, wilh the male 

 01 (uu. The detached Agtire repreaenta one of theae organ*. 



On thin subject Professor Bell remarks :- -" When we conni,!, T i lie 

 aluiOHt endless diversity of form mi'liT whieli the specie* conn. 

 this clan of animals appear, the astonishing discrepancy which 

 in the forum and relative proportions of the ditlcreiit regions of tl 

 body, and other parts of their organisation for the performance of 

 office* and functions equally various, and see that all these diversities 

 are produced only by modifications of a typical number of part*, we 

 cannot but be struck by so remarkable and interesting an illustration 

 of the great economical law, as it may be termed, that the ta/, ,,,! 

 frucfure of any group being yiten, the different habiti of tit component 

 tlfdet or minor groupt are provided fur, not by the creation of new 

 organ* or the detraction of othtri, but by the modification in form, 

 tincture, or place, of organ* typically belonging to the group." 



One of the necessary consequences of the condition of these 

 animals inclosed in a hard shell is the power they possess of throwing 

 it off. If this were not the case all growth would be stopped, except- 

 ing increase of thickness in the shell by a succession of secretions from 

 below. To allow therefore room for the expansion and growth of 

 the body and limbs, a provision for their increase is made by means 

 of moulting, which, as a general rule, is more frequent the younger 

 the animal is, as indeed might be expected. Thus eight moults in 

 the short space of seventeen days have been observed in a yi>mi^ 

 Dapknia. [liKANcuioroUA.] It can be easily observed in the Common 

 Crab. [CAN. nt.) 



In Attacut Jluviatilit, the moult, or Ecdysis, as this process is called, 

 is preceded by a few days of fasting and sickness, and at that time 

 the carapace becomes loosened from the corium to which it W:LI 

 attached. The corium begins forthwith to secrete a new shell, which 

 U at first soft and membranous, becomes gradually harder and hurdrr, 

 and is at last calcareous. When all connection with the old shell in 

 broken off, and the corium has completely secreted the new mem- 

 branous envelope, the animal begins to set about freeing iUelf from 

 the old incumbrance, and becomes very restless, the symptoms of 

 inquietude increasing in proportion as the time for emancipation 

 draws nigh. It rubs its legs one against the other, and finally throws 

 itself on its back. In that situation it begins to shake itself and swell 

 itself out, till it tears the membrane which connects the carapace 

 with the abdomen, and begins to raise the former : then it rests a 

 while. Alternations of agitation and rest succeed each other :,t inter- 

 vals of longer or shorter duration, the carapace is completely raised, 

 the head, the eyes, the antenna 1 , are extricated. The greatest dif- 

 ficulty occurs in freeing the extremities, nor could they be extricated 

 at all did not the old covering split longitudinally : and indved it 

 frequently happens that the Crawfish leaves a limb or two behind ; 

 and is sometimes so fettered, that it perishes front inability to extri- 

 cate itself. The abdomen is the last division of the body freed, :iu<! 

 the whole change generally takes place in half an hour. Four-and- 

 twenty-hours, or two or three days at furthest, are necessary for the 

 conversion of the soft and membranous integument which sheathes 

 the corium or naked body into a firm calcareous case similar to the 

 last, and presenting the same appendages, even to the hairs ; although 

 M. Milne-Edwards has stated that these hut organs are not formed 

 within the old ones, as supposed by Reaumur, but exist ready -t< 

 in the new envelope, turned in towards the interior like the fim-< 

 a glove turned in upon itself. 



Mr. Spence Bate of Plymouth, who has very successfully M 

 the Omtacea, states that he has confirmed the original observation 

 of Reaumur. 



M. Milne-Edward* observes that the time occupied in the business 

 of throwing off the shell varies considerably in different, |>ecic,s, and 

 that it also depends on atmospheric influences ; and this obsorvutii n 

 applies equally to the number of day* required for giving the new 

 tegumentary sheath the oonsiatency of the old obeli ; and he adds, 

 that in the whole of the species which have been duly watched, 

 especially those found on the French shores, the period which precedes 

 and that which follows the Eodysis is a period of inquietude and 

 disorder. The muscle* are then flaccid, the flesh is soft and watery, 

 and the animal* are considered unwholesome and unfit for food. An 

 exception to this remark occurs in the Land-Crabs ((Jecarcintu), which, 

 according to the testimony of all who have spoken and written on the 

 subject, are never so delicious u during the season of change. 



