HARDWICKE'S SCIENCE-G SS/P. 



85 



much longer prolonged, will be separated from each 

 other. There are a vast number of these ambu- 

 lacral suckers on the entire test, and by their aid the 

 creature not only drags itself along, but anchors itself 

 to the rocks, and so tenaciously, that it requires con- 

 siderable force to detach it ; indeed, sooner than let 

 go its hold, I have found that it will allow the 

 suckers and tubes to be torn from it, and they have 

 been left on the bottom of the plate to which it had 

 been clinging. In fact this is the best way of obtain- 

 ing specimens for microscopic investigation. By 

 means of those on the upper portion of the shell the 

 animal is able to right itself if thrown on what we 

 may call its back, and by their aid also it can, and 

 does often, completely cover itself with pieces of sea- 

 weed, for the purpose, I presume, of concealment 

 from its enemies. 



The method by which these suckers are extended 

 or retracted at the creature's will is interesting. In the 



muscular bag filled with fluid is attached to the same. 

 When the sucker is to be protruded the muscles of 

 the interior bag contract, whilst the longitudinal ones 

 of the tube are relaxed, and consequently the fluid 

 expelled from the bag passes through the Vo pores 

 and entering the tube extends it. When it is to be 

 retracted, the process is of course reversed ; the 

 longitudinal muscles of the tube contracting, whilst 

 those of the bag relax, so that the fluid can re-enter it. 



I need scarcely remark that in the sucker of the 

 Echinus we have another example of a mechanical 

 power in nature that has existed for ages, and that it 

 has been unconsciously reproduced in the school-boys' 

 well-known leathern sucker. 



Let us now turn our attention to those extraordinary 

 appendages, the pedicellariae, which have always been, 

 and still are, a puzzle to naturalists. What their 

 functions may be, and what use they are to the 

 animal, is still a question which will be alluded to 



' - M 



Fig. 83. — Fedicellaria globifera. 



Fig. 84. — Fedicellaria stci-cophylla, open and closed. 



first place it may be seen under the microscope that the 

 tubes are furnished with both longitudinal and annular 

 muscles, the former for lengthening and shortening 

 them, the latter for increasing or diminishing their 

 calibre. I have said that there are five pairs of 

 ambulacral rows of pores. Now if a portion of one of 

 these meridianal primary rows is carefully examined, 

 it will be found to consist of numerous subordinate 

 diagonal ones, each of which is made up of three 

 pairs of pores. The tube of the sucker covers and 

 embraces one of these pairs, and within the test a 



Fig. 85.— Single blade of 

 Fig. 81. (Fedicellaria 

 triphylla.) 



presently. I will only remark, 

 here that similar organs are 

 found in some of the star- 

 fishes, and in a few of the 

 polyzoa. The Echinus has no 

 less than four different kinds 

 of pedicellarias, distinguished 

 by the names of Triphylla, 

 Tridens, Globifera, and Ste- 

 reophylla. I have found them 

 all, with the exception of 

 Globifera, on the naked mem- 

 brane surrounding the mouth, 

 the latter seems to be con- 

 fined to the bases of the spines, whilst Triphylla, by 

 far the most abundant, is also scattered generally over 

 every portion of the shell. Although the form and 

 size of the different species differ considerably, their 

 general plan and structure are identical. A calcareous 

 and more or less fibrous stem, enlarged at either end 

 like a double drum-stick, is anchored at its base to the 

 naked membrane round the mouth, or to the shell by 

 its sarcodic envelope, which, clothing the entire length 

 of the stem, protrudes far beyond its free end, except 

 in the case of Globifera, forming an extensile flexible 



