1892.J Cavity of the Larva of Palsemonetes varians. 339 



dorsal line, where it meets its fellow of the opposite side. The two 

 bladders grow backwards over the stomach, subsequently fusing in 

 the middle line to form the unpaired nephroperitoneal sac. This 

 mode of development confirms the view as to the nature of the latter 

 sac already arrived at by Weldon and Marchal from a comparative 

 study of the renal organs of Decapods. 



The Shell Gland. In a figure of a Callianassa larva in the My sis 

 stage, Glaus* inserts and names the shell gland, opening at the base 

 of the second maxilla. This is, I believe, the only recorded instance 

 of the gland having been recognised in a Decapod, unless, indeed, the 

 " segmental organ " described by Lebedinskif as opening at the base 

 of the first maxillipede of the larva of Eriphya spinifrons, and com- 

 municating with the body cavity, be the same organ. 



In late embryos, and at the time of hatching of the larva, the shell 

 glands are the functional kidneys of Palcemonetes and Palcemon, the 

 green gland being still without a lumen. The shell gland of Palce- 

 monetes consists of a comparatively short renal tube, with a consider- 

 able lumen, which communicates internally with an end sac, and 

 opens externally at the base of the second maxilla. The general form 

 of the tube may be expressed by saying that it is Y' SQa P e d> * ne * wo 

 arms of the Y being in a horizontal plane, with the end sac attached 

 to the internal one, whilst the leg of the Y ^ s curved in a vertical 

 plane, the concavity looking downwards and backwards. The histo- 

 logical structure of both end sac and renal tube is similar to that 

 described by GrobbenJ for the green gland of My sis. The entrance 

 from the end sac to the tube is guarded, however, by a valve, formed 

 of elongated cells of the end sac, which does not appear to have been 

 found in other forms. 



I have detected no trace of the shell gland in young adults. 



ill. The Body Cavity. 



The Anterior Eegion of the Thorax. A transverse section through 

 the region of the second maxillae of a Palcemonetes larva, which is a 

 few days old, shows that the cavity enclosed by the external chitin 

 and ectoderm may be divided into four regions : a dorsal sac, sur- 

 rounded by a definite layer of epithelium, and within which the 

 cephalic aorta lies, but which does not itself contain blood ; a central 

 cavity, in which the liver, intestine, and nerve cord, are found ; two 



* Claus, C., " Neue Beitrage zur Morphologie der Crustaceen." ' Arb. Zool. 

 lost. Wien,' vol. 6, 1886. 



t Lebedinski, J., " Einige Untersuchungen iiber die Entwicklungsgeschichte der 

 Seekrabben." ' Biol. Central bl.,' vol. 10. 1890. 



I G-robben, C., " Die Antennendruse der Crustaceen." ' Arb. Zool. Inst. Wien,' 

 vol. 3, 1881. 



