Body- Cavity of the Larva <?/ Palcemonetes varlans. 237 



towards tlie midtlle ventral line of the body, then upwardg, 

 within the oesoj)iiageal nerve-ring and anterior to the oesopha- 

 gus, to tlie middle 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 3fysis stage Claus * 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 recog- 

 nized in a Decapod, unless, indeed, the " segmental organ " 

 described by Lebedinski f as opening at the base of the first 

 maxillij)ede of the larva of Eriphya spinifrons and communi- 

 cating 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 

 Pala^mon, the green gland being still without a lumen. The 

 shell-gland of Palcemonetes consists of a comparatively short 

 renal tube with a considerable 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-shaped, the two arms of the 

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

 internal one, whilst the leg of the Y is curved in a vertical 

 plane, the concavity looking downwards and backwards. The 

 histological structure of both end sac and renal tube is similar 

 to that described by Grobben | for the green gland of Mysi's, 

 The entrance from the end sac to the tube is guarded, how- 

 ever, by a valve formed of elongated cells of the end sac, 

 which docs not appear to have been found in other forms. 



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



II. The Body- Cavity. 



The Anterior Region of the Thorax. — A transverse section 

 through the region of the second maxillae of a Palcemonetes 



* Claus, C, " Neue Beitrage zur Morphologic der Crustaceen," Arb. 

 Zool. Inst. Wien, vol. \i., 1886. 



t Lebediuski, J., " Einige Uutersuchungen iiber die Entwicklungs- 

 geschichte der Seekrabben," Biol. Centralbl. vol. x., 1890. 



X Grobben, C, *' Die Antennendriise der Crustaceen," Arb. Zool. Inst. 

 Wien, vol. iii., 1881. 



