WYVILLE THOMSON, ON SYNAPTA INU.ERENS. 141 



During the years 1849, 1850, 1851, Johannes Miillermade 

 a most important series of observations. He referred several 

 closely allied larvse which he met with at various localities on 

 the Mediterranean and Adriatic to the Holothuridae, and 

 grouped them, from a common peculiarity in form, under the 

 general term " Auricularia ." 



Externally, an Auricularia is somew^hat like a frilled toilet 

 pincushion. It has a dorsal and a ventral surface, and two 

 lateral surfaces; the latter deeply grooved. The line of 

 junction between the dorsal and ventral, and the lateral 

 faces is continued into an undulating border, prolonged into 

 various appendages. The length of the body is nearly twice 

 its width, and its Avidth about twice its thickness. At one 

 end the dorsal, the ventral, and the lateral surfaces form a 

 four-sided pyramid, and at the opposite extremity, which is 

 thicker and softer, the dorsal surface passes round to join the 

 ventral ; the dorsal and ventral fringes thus becoming con- 

 tinuous, and spreading out right and left into ear-like 

 appendages. The dorsal surface is smooth ; the ventral sur- 

 face is bisected by a transverse groove, at the bottom of which 

 lies the mouth. The muscular oesophagus opens into a dis- 

 tinctly dilated stomach, and a short curved intestine, follow- 

 ing the median line, curves round to the anus, which is 

 placed on the ventral surface, close to the thickened (posterior) 

 extremity of the body. The ciliated band so characteristic 

 of Echinoderm-larvpe, coincides throughout with the frilled 

 border. It is continuous along the margin of the dorsal 

 surface ; it passes round the auricular appendages, following 

 the undulations of the border and crossing the ventral sur- 

 face, along the posterior edge of the oral groove ; at the apex 

 of the pyramidal extremity it also becomes deflected on either 

 side to the ventral surface, passing back along the inferior 

 angles of the pyramid, and crossing by the anterior edge 

 of the oral furrow. As Mr. Huxley remarks, notwith- 

 standing the appearance of longitudinal prolongation, the 

 ciliated fringe, crossing the body before the mouth and 

 before the anus, is, so far as the axis of the alimentary canal is 

 concerned, actually transverse, encircling it only once. I do 

 not, however, attach much significance to the distribution of 

 these fringes. 



Before the Auricularia undergoes any metamorphoses, 

 a flask-shaped vesicle appears above and somewhat before 

 the stomach, connected by a delicate tube, with an um- 

 bilical depression on the dorsal surface of the Auricu- 

 laria. A calcareous ring, sending off spiny branchlets, 

 shortly encircles this dorsal tube about the middle of 



