PEOPAttATlON OF CERTAIN ECHINODEEMS. 57 



tection, and for nutrition only indirectly througli the mucus 

 exuded from the surface of her perisom, and through the currents 

 of freshly aerated water containing organic matter brought to 

 them or driven over them by the action of her cilia. 



Animals hatching their eggs in this way ought certainly to give 

 the best possible opportunities for studying the early stages in 

 the development of their young. Unfortunately, however, this 

 is a kind of investigation which requires time and stillness and 

 passable comfort ; and such are not the usual conditions of a 

 voyage in the Antarctic sea. Specimens have been carefully pre- 

 served with the young in all stages ; and I hope that a careful 

 examination of these may yield some further results. 



Although the principle and the leading features of the process 

 are the same in all, the details vary greatly in the different groups. 

 My present object is to give a preliminary sketch of some of the 

 more remarkable modifications. In the absence of a sufficient 

 supply of books of reference, I cannnot vouch for the accuracy of 

 specific determinations ; the names which I have given to the 

 species referred to must therefore be taken in some cases as pro- 

 visional. I will select examples from the leading groups in order. 



I. HOLOTHTJEOIDEA PEDATA. 



Cladodactyla crocea, Lesson, sp. (fig. 1). An elegant cucumber- 

 shaped sea-slug, from 80 to 100 miilims. in length, by 30 millims. 

 in diameter at the widest part, of a bright saffron-yellow colour, 

 very abundant, adhering to the vast fronds of Macrocystis in from 

 five to ten fathoms water in Stanley Harbour at East Falkland 

 Island. The mouth and arms are terminal ; ten long delicate 

 branched oral tentacles, more resembling in form and attitude 

 those of Ocnus than those of the tj^icdl CucumaricB, surround the 

 mouth : the perisom is thin and semitransparent ; and the muscular 

 bands, the radial vessels, and even the internal viscera can be plainly 

 seen through it. The three anterior ambulacral vessels are ap- 

 proximated ; and on these the tentacular feet are numerous and well 

 developed, with a sucking-disk supported by a round, cribriform, 

 calcareous plate, or more frequently by several wedge-shaped 

 radiating plates arranged in the form of a rosette ; and these three 

 ambulacra form together, at all events in the female, a special 

 ambulatory surface. The two ambulacral vessels of the bivium 

 are also approximated along the back ; and thus the two inter- 

 auibulacral spaces on the sides of the animal, between the external 



