THE OCELOM AND NEPHRIDIA OF PAL^MON SEERATUS. 163 



The considerations here shortly summarised have led to the con- 

 clusion that the Arthropods must be regarded as a group of animals 

 in which a coelom, comparable with that of Chgetopods^ Molluscs, 

 &c., has either permanently retained, or has secondarily acquired 

 the condition of existence as a mere appendage of the nephridium, 

 the functional body-cavity being a space of an entirely different 

 nature. 



Observations recently made in the Laboratory of the Marine 

 Biological Association at Plymouth have led me to believe that the 

 coelom of Palsemon, at least, is much more highly developed than is 

 generally supposed ; and to take a view of the structure of the nephri- 

 dium which differs considerably from that enunciated by Grobben. 



The observations referred to were made upon the common English 

 P. serratus (Fabr.), and were suggested by an attempt to repeat the 

 experiments on excretion recently described by Kowalewsky,* who 

 has shown that the renal tubules of P. Treillianus send branches 

 into the thorax, — branches which extend back as far as the peri- 

 cardium (1. c, p. 37). 



Kowalewsky's observations were made by injecting various colour- 

 ing matters into the tissues of the prawn ; and these colouring 

 matters, being absorbed by the renal tissues, stained such tissues 

 deeply, and so made them easy of observation. 



If a small quantity of a 1 per cent, solution of indigo-carmine 

 be injected into the tissues of a healthy P. serratus, the colouring 

 matter passes quickly into the venous sinuses, and in this way the 

 gills speedily acquire a blue colour. Kowalewsky has demonstrated 

 the presence in the gills of P. Treillianus of certain cells which take 

 up colouring matters, and which have an acid reaction ; so that a 

 neutral or alkaline solution of litmus, passing from the body into 

 the branchiae, becomes reddened on absorption by these cells. I 

 have been unable to satisfy myself of the existence of these cells in 

 P. serratus, in which the blue colouration observed after injections 

 of indigo-carmine seems to be due simply to the presence of colouring 

 matter in the blood passing through the vascular and transparent 

 lamellee of the branchial plumes. 



Be this as it may, however, the colouring matter, after appearing 

 in the gills, gradually leaves these organs and is more and more 

 completely taken up by the coelomic and nephridial cells. Some 

 hours after an injection the prawn is seen to have lost all colour, 

 except in the region of the kidneys and in the median dorsal portion 



the Morphological Laboratory in the University of Cambridge, vol. iv, pt. i, and Quart. 

 Journ. Micr. Sci., vol. xxvii, 1887, pp. 533, et seq. 



* Kowalewsky, A., Ein Beitrag zur Kenntniss der ExJcretionsorgane, Biologische 

 Centralblatt, Bd. ix, Nr. 2, March, 1889. 



