164 THE CCKLOM AND NBPHKIDIA OF PALJ]MON SERRATUS. 



of the cephalotliorax ; these portions of the body being after an in- 

 jection of suitable strength intensely blue. The colouring matter 

 remains in these regions for some time, presumably until its final 

 excretion through the nephridia 



If a prawn, in which indigo-carmine has been absorbed in the 

 manner just described, be dissected in strong alcohol, it will be seen 

 that the blue area of the thorax communicates by a deeply stained 

 band of tissue with each nephridium ; and if the blue structures be 

 carefully dissected out and removed from the body they will present 

 the appearance which is shown in fig. 1. The cephalothorax is then 

 seen to contain a large delicate sac [coe.), whose walls consist of a 

 flat pavement epithelium with a slight investment of connective 

 tissue. This sac extends from the front of the head, immediately 

 behind the rostrum, to the anterior extremity of the generative gland, 

 to which it is closely attached (fig. 1, ov.). Dorsally the sac is 

 covered only by the integument, from which, however, it is separated 

 in the middle line by the ophthalmic artery (a. o.). 



The walls of the cephalothoracic sac have the power of absorbing 

 indigo- carmine in considerable quantities ; and it is this property 

 which causes the appearance of a dark blue patch in the cephalo- 

 thorax after injection. The cavity of the sac is filled with a clear 

 fluid, which is not blood, and which does not, at least for some time 

 after the injection of indigo-carmine into the tissues, become coloured 

 blue. 



At its anterior extremity the cephalothoracic sac gives off a pair 

 of tubular processes, one on each side, each of which dips down- 

 wards and passes between the oesophageal nerve-commissure and 

 the great antennary muscles to open into the urinary bladder of its 

 own side (figs. 1 and 8) . A perfect communication is thus established 

 between the nephridia and the cephalothoracic sac. 



It is evident that, if the observations here recorded are correct, 

 we have a sac in close contact at one extremity with the generative 

 gland and in communication at the other with the nephridial tubes, 

 and so with the exterior. This sac is further devoid of any com- 

 munication with the system of blood-spaces. That is to say, we have 

 a sac precisely similar in all its relations to the coelomic sac of a 

 Mollusc — especially to that of such a form as Octopus.^ 



The connection of the coelom with the generative gland is so close 

 as to render it perfectly probable that the cavity of the gonad and 

 of its ducts may at an earlier stage in ontogeny be continuous with 

 that of the coelomic sac. 



The junction between coelom and nephridia is effected, as has 



* Compare the account of the renal and coelomic organs of this form given by Grobben, 

 Arb. ^ool. Inst. Wien, Bd. v, 1884, 



