SEA-URCHINS, STARFISH, AND BRITTLE -STARS. 145 



flukes project from the surface and cling to the hand, as 

 under natural conditions they do to the sand. This Holo- 

 thurian, then, is literally and not metaphorically anchored to 

 the sand, the anchors being numerous and scattered all 

 over the body. If you examine a fragment of the skin 

 under a strong lens or a low power of the microscope, you 

 will see that each anchor is connected with a little plate 

 perforated by seven or nine holes, and that it can move 

 on this plate as on an axis. Plates and anchors together 

 represent the limy deposits of Cucumaria, and so the limy 

 skeleton of other Echinoderms, and are exceedingly character- 

 istic of Synapta. After having once been seen they can 

 hardly be mistaken for anything else. I once knew a 

 learned professor who was a great admirer of these anchors, 

 and used to bring them out with the utmost regularity 

 whenever he presided over a zoology examination. Both 

 they and their owner are a little out of the way of ordinary 

 zoology students' observations, so the candidates came to 

 grief time after time through their wild shots on the 

 subject, until the professor was ill-advised enough to remark 

 in a public address on the ignorance of Synapta which 

 prevailed among zoological students. After that all institu- 

 tions which sent up candidates to the public examinations 

 purchased a slide displaying the anchors, and so succeeded 

 in passing their students without the trouble of going to 

 dig for Synapta, or studying its structure. 



Associated probably with the burrowing habit of Synapta, 

 we have the interesting fact that the tube-feet are absent 

 from the body, and are represented only by the crown of 

 tentacles at the anterior end. In Cucumaria the tentacles 

 are also modified tube-feet, and these are the only ones 

 which can be described as well developed. In Synapta the 

 tentacles are the only representatives of tube-feet present at 

 all. The statement that in Cucumaria and Synapta, as in 

 Holothurians in general, the tentacles are modified tube-feet 

 is not a mere assertion, but is justified by the relation of 

 these tentacles to the ambulacral system, a relation easily 

 studied in the larger Holothuria by dissection. 



The only species of Synapta usually to be found between 

 tide-marks is S. inhcerens, recognised by its twelve tentacles, 

 each with six or seven finger-like processes at either side, 



