ON OUR PRESENT KNOWLEDGE OF THE CRUSTACEA. 233 



111 the brephalus of Paltemon, whicli we have carefully studied in a 

 fresh and living state, we liave not been able to detect any vibratile cilia 

 within the stomach, but have observed that the outer wall has a strong 

 and persistent power of contracting upon itself, and so forcing the con- 

 tents of the stomach in a constant motion. 



M. Gerbe (loc. cit.) also states that the liver consists of two simple cteca, 

 one on each side, ' manifestly a diverticulum of the intestinal tube, with 

 which it has wide communications ; by ramifying it forms a hollow tree, 

 at the base of which oscillate the vitelline globules, which the umbihcal 

 vesicle pours into the pyloric portion of the intestine.' 



He also states that in whatever manner the respiratory functions may 

 be performed in the adult crustacean, all have a tegumentary respira- 

 tion in the brephalus condition, whether it be in the zoaja or megalop stage. 



He has observed the brephalus of Eomarus to possess a rudimentary 

 branchial apparatus quite unfit to perform any functions, while the bre- 

 phali of other genera are absolutely destitute of such organs, and some do 

 not obtain them until after several moults. 



This want of branchial respiration necessitates a distinction m the 

 character of the circulation in the younger, as compared with that of 

 the adult forms of Crustacea, that is as between those that have none and 

 those that have matured branchial organs. 



In the brephali of Maia, .Forcellana, Crangon, Palamon, Palinurus, 

 Eomaru?, Cancer, &c., the blood which the arteries have distributed to the 

 different parts of the body returns entirely, directly to the heart, and this 

 condition continues for a considerable time. ' It is,' he says, ' only after 

 the third moult, in the most perfect brephalus of the species inhabiting our 

 seas, that of the lobster, that a few globules are diverted from the original 

 general circulation to penetrate into the nascent branchiae. All the 

 arteries open directly into the venous passages by an aperture more or 

 less dilated into a trumpet-like form. 



' In somelarvee the abdominal artery may present a sort of sphincter m 

 its course, at some distance from the central organ of circulation ; this, 

 by contracting, temporarily suspends the flow of blood to the hinder 

 parts.' This remarkable peculiarity exists not only in the larva of the 

 lobster, but also in those of the Porcellance, and may be found most pro- 

 bably in the many other genera, as M. Gerbe has observed the circulation 

 iu the last somite of the pleon of the brephalus of Cancer, Carchms, and 

 Palcemon to have interruptions. 



The same author states that, ' Although the transitory spines which 

 arm the thorax ' (carapace) ' of some species do not receive any arterial 

 branch, a complete circulation is established in their cavity. Some of the 

 globules which the venous lacunae convey to the heart, make a digression 

 into these transitory appendages, traverse nearly their whole length, and 

 return by a parallel course into the lacuna from which tliey started. 



M. Felix Plateau, of Ghent, has, through the agency of a graphic 

 method, succeeded in obtaining a delineation of the heart's action in the 

 crayfish. A curve is obtained, of which the ascending portions correspond 

 to diastole, and the descending to systole, contrary to w^iat obtains in the 

 heart of vertebrate animals. 



It is, he says, strikingly like the trace of the contraction of a 

 muscle — a rapid, almost sudden ascent, with a flat summit, then a 

 gradual descent, at first quicker, then slower. This, however, does not 

 represent the whole truth; it is possible also to demonstrate a wave 



