ON OUK PRESENT KNOWLEDGE OF THE CRUSTACEA. 235 



always fall of air, whicli the animal had not the power to expel, and even 

 after submersion of the animal in water for three days some Uca had still 

 a considerable quantity of air in the upper part of the branchial vaults. 

 By the researches of Milne-Edwards and Andouin, we know that the 

 ai-terial blood traverses vessels which become smaller and smaller, but is 

 not taken up by the capillary veins, that it passes into some lacuna; in com- 

 munication with the general cavity, and a portion of the branchiae, and 

 that after it has been revivified in these organs it is taken up by vessels 

 which carry it into the pericardiac chamber, which is no other than an 

 auricula : from thence into the heart. A coloured injection demonstrates ' 

 if the canals of the resj^iratory membranes are arterial or venous. It also 

 shows a network of extreme beauty that ramifies upon the vault, both 

 on the internal and external parietes of the respiratory chamber. This 

 network is regularly developed, and commences in a large sinus situated 

 in the anterior part behind the orbital cavity. It divides into three 

 vessels which ramify on the vertical septum (cloison), and another vessel of 

 very large diameter which traverses the angle of connexion between the 

 carapace and the lateral walls of the branchial cavity. Of the other 

 vessels of less importance, one of which should be noticed, it curves and 

 ramifies in the folded membrane described by Milne-Edwai'ds and Andouin. 

 All these vessels send forth a number of branches which resolve into 

 capillaries that terminate in small irregular polygonal spaces, which are 

 the true lacunae ; but from these lacunte other equally delicate vessels take 

 their departure. They may be observed to enlarge and open into still 

 larger vessels, which still increase in size and open in their turn into a 

 large trunk, which opens into an enormous sinus situated posteriorly to 

 the pereion (or body of the animal) near where the pleon commences, 

 about a centimetre within and above the basal portion of the last pair of 

 feet. This large sinus traverses the vertical septum (cloison) and opens; 

 into the auricle. 



A coloured injection forced into the sinus gives evidence of vascular 

 network nearly symmetrical with that observed so regularly di.^played on 

 the walls of the respiratory chamber. Of these vessels one ramifies on the 

 vertical septum, the other, which is of considerable diameter, winds upon 

 the roof of the chamber. Another equally worthy of notice is situated in 

 the angle of the internal membrane folded horizontally on the walls of the 

 chamber. 



There consequently exists, according to M. Jobert, in the parietes of 

 the respiratory chamber a double system of vessels connected together by 

 an intermediate capillary network inducing communication direct between 

 the heart and the general cavity. 



The air which is contained in the respiratory chamber never stagnates, 

 but is renewed very regularly by the aid of a true movement of inspiration 

 and expiration. The expiratory orifice of the ch.amber offers nothing very 

 particular ; whereas the inspiratory, in addition to that v/hich is situated at> 

 the anterior part of the first pair of feet, is supplemented by others smaller 

 but still important, situated between the third and fourth and posterior 

 pairs, having the orifices externally hid by long hairs. It is to the 

 vertical septum that the power belongs that induces the alternating 

 movements of inspiration and expiration, and that iinder the influence of 

 the central organ of circulation. In Uca, where the heart is of consider- 

 able size, we may observe at the period of the afflux of the blood into 

 the cavity a corresponding movement outside the vertical septum which 



