Mr. P. H. Gosse on Sarcodictyon catenata. 277 



of rather more than one-fourth of an inch, with a thickness of 

 about one-sixteenth (see fig. b). 



The disk is surrounded by eight marginal tentacles, which 

 often extend to one-fifth of an inch in length : their bases are 

 thick and contiguous; their figure that of a cone much pro- 

 duced, and terminating in an exceedingly attenuate point. Each 

 tentacle is fringed along each of its two lateral faces with a row 

 of pinnae, about fourteen in number in each row. These are 

 conico-cylindrical processes, of extreme delicacy, longer in the 

 middle of the row, and diminishing to each extremity. 



The pinnse are hollow throughout, with very thin parietes : 

 their cavities communicate freely with that of the tentacle, of 

 which they may be considered as csecal appendages. They are 

 composed, like the tentacles, of contractile tissue, doubtless 

 muscular, and are capable of great elongation, or, at pleasure, 

 of reduction to mere warts. The exterior surface of the pinnse 

 is studded with oblong tubercles, which are set on in a spiral of 

 about five whorls, the extreme tip being invariably crowned by 

 one of globose shape (see fig. c). Under the pressure of the 

 compressorium, with a magnifying power of 600 diameters, 

 these tubercles were seen to be composed of granular tissue, 

 enclosing moderately few cnidse, pointing outwards, and bearing 

 on minute eminences of their surface the fine appendages which 

 my friend Dr. T. Strethill Wright has named palpocils* (see 

 fig. d). The cnidse are ovate, arcuate, and very minute, averaging 

 •0004 inch in length and *0001 inch in thickness. The tubercles 

 have a decidedly spiral arrangement on the pinna, though the 

 pinnse are strictly bifarious on the tentacle. 



Interiorly the pinnse are richly ciliated ; and corpuscles in the 

 peritoneal fluid are seen forcibly driven to and fro by the con- 

 flicting currents. The epithelial lining of the tentacles is simi- 

 larly clothed with cilia ; but the currents here are chiefly mani- 

 fest in the basal region, and their course is regularly downward 

 into the interseptal cavities. 



The disk presents nothing remarkable ; it is smooth and trans- 

 lucent. The mouth is encircled by a thin lip, which is capable 

 of protrusion in the form of a low circular wall. A good micro* 

 scopic observation, obliquely down into the stomach, showed me 

 that (on that side, at least ; I can say nothing of the other) there 

 is one gonidial groove, of which the edges were sometimes brought 

 temporarily into mutual contact for a portion of their length, 

 forming thus a tube, and at other times were widely separated — 

 forming a broad and shallow channel. I could see no appear- 

 ance of gonidial tubercles. The groove thus seen coincides with 

 one of the extremities of the line which a transverse section 

 * Edinb. New Phil. Journ. for April 1857. 



