ECHINODERMATA. 153 



is altogether distinct from that of the pluteus) is formed at that side of 

 the granular mass over which the shell is last extended; and the first in- 

 dication of it consists in the appearance of the five calcareous concretions, 

 which are the summits of the five portions of the frame-work of jaws and 

 teeth that surround it. All traces of the original pluteus are now lost"; 

 and the larva, which now presents the general aspect of an Echinoid 

 animal, gradual augments in size, multiplies the number of its plates, 

 cirrhi, and spines, evolves itself into its particular generic and specific 

 type, and undergoes various changes of internal structure, tending to the 

 development of the complete organism. 



a. An excellent summary of the developmental history of the several Echino- 

 derm-types, with references to the principal Memoirs which treat of it, will be 

 found in Chap. xx. of Mr. Balfour's "Comparative Embryology." In collecting 

 the free-swimming larvae of Echinodermata, the Stick-net should be carefully 

 employed in the manner already described ( 217); and the search for them is of 

 course most likely to be successful in those localities in which the adult forms of 

 the respective species abound, and on warm calm days, in which they seem to 

 come to the surface in the greatest numbers. The following mode of preparing 

 and mounting them has been kindly communicated to the Author by Mr. Percy 

 Sladen: "For killing and preserving Echinoderm zooids, I have come to prefer 

 either Osmic acid or the Picro-sulphuric mixture of Kleinenberg ( 199, e) of one- 

 third strength. The latter, of course, destroys all calcareous structures, but the 

 soft parts are preserved in a wonderful manner. If the diluted Kleinenberg's 

 mixture is used, let the zooids remain in it for one or two hours; then wash them 

 thoroughly in 70 per cent Spirit until all trace of acid is removed; then stain; 

 then again wash in 70 per cent Spirit, transfer them to 90 per cent Spirit for 

 some hours, and lastly to absolute Alcohol. Transfer them from this to Oil of 

 Cloves; and finally mount in Canada balsam in the usual manner. If Osmic acid 

 be used, place three or four of the living zooids in a watch-glass of sea- water, and 

 add a drop of the 1 per cent solution. They should not remain even in this weak 

 solution for more than a minute; and should then be thoroughly washed in a 

 superabundance of 35 per cent Spirit, to prevent the deposit of crystals of salt 

 consequent on the action of the osmic acid. Then transfer the specimens to 70 

 per cent Spirit; and proceed as in the other case. 



546 . One of the most interesting to the Microscopist of all Echino- 

 dermata is the Antedon l (more generally known as Comatula), or 

 'feather-star' (Fig. 378), which is the commonest existing representative 

 of the great fossil series Crinoidea, or ' lily star,' that were among the 

 most abundant types of this class in the earlier epochs of the world's his- 

 tory. Like these, the young of Antedon is attached by a stalk to a fixed 

 base, as shown in Fig. 379; but when it has arrived at a certain stage of 

 development, it drops off from this like a fruit from its stalk; and the 

 animal is thenceforth free to move through the ocean-water it inhabits. 

 It can swim with considerable activity; but it exerts this power chiefly 

 to gain a suitable place for attaching itself by means of the jointed 

 prehensile cirrhi put forth from the under side of the central disk (Fig. 

 378); so that, notwithstanding its locomotive power, it is nearly as sta- 

 tionary in its free adult condition, as it is in its earlier Pentacrinoid 

 stage. The pentacrinoid larva 2 first discovered by Mr. J. V. Thomp- 



1 The Author has found himself obliged, by the accepted rules of Zoological 

 nomenclature, to adopt the designation Antedon, instead of the much better known 

 and very appropriate name given to this type of Lamarck. See his ' Researches 

 on the Structure, Physiology, and Development of Antedon rosaceus,' Part. I., in 

 " Philos. Transact.," 1866, p. 671. 



2 The Pentacrinoid larvae of Antedon have been found abundantly (attached to 

 Sea-weeds and Zoophytes) at Millport on the Clyde, and in Lamlash Bay, Arran; 

 in Kirkwall Bay, Orkney; in Lough Strangford, near Belfast, and in the Bay of 

 Cork; and at Ilfracombe, and in Salcombe Bay, Devon. 



