22 



ON THE EMBRYOLOGY OF ECHINODERMS. 



ment of these two forms was apparently so contrary. Let us take the Plutcus at the 

 time of the appearance of the young Ophiuran, and deprive it of its arms, we should 

 soon find our Pluteus in a condition in which the nomadic and sedentary mode of 

 development could not be distinguished ; showing us that for Ophiurans, as well as 

 for Starfishes, these two modes of growth, at first so different, reach, early in the 

 development of the young, stages which are identical* 



HOLOTHURIANS. 



Cuvieria Fabricii Dub. et Kor. 



In Holothurians the two modes of development seem to combine in a very remark- 

 able manner. The larva has short arms only in the early stages ; it remains nomadic 

 after they have disappeared, when it would be very difficult to tell by which of the 

 two modes the young Holothurians have been developed. See Muller's figures, in 

 which the Auricularia approaches the M Walzenformige n form, fourth Memoir, Plate I. 

 From the young Holothurians which I have myself observed I am not able to say 

 anything concerning the water-tubes, and must therefore make a comparison of the 

 Memoirs of Muller with what has been suggested here. Although we have a Sy- 

 napta and a Chirodota (Cauclina arenata Stimp.) which are very common here, all my 

 attempts at artificial fecundation, or at finding their plutean stages with the other 

 Echinoderm larva?, have completely failed. The only Holothurian of which I have 

 seen the young is Cuvieria, which is tolerably abundant in deep water off Nahant, 

 and of which the young, in the more advanced stages only, however, are found from 

 June to October. The study of the development of an Auricularia witli reference to 

 the part the water-tubes play in this would be particularly 



Holothurians are the only Echinoderms studied by Muller in which he distinctly 

 says that the young Holothurian resorbs the whole of the pupa, as he calls the 

 envelope of the Holothurian, and which lose nothing during the development. On 



of this resorption, he considers the plan of the Holothurian development 



o 



be something special. I trust I have made it sufficiently clear that resorption takes 



* The fact that Ophiopholis lays its eggs in hunches seems to lessen the difference between the Echinoderms 

 which lay eggs and those which are viviparous, or retain the eggs in bunches in a sort of pouch at the base of 

 the anus, as m fig. 34, which figure shows the manner in which a small Asteracanthion, allied to A. Mulleri 

 Sars, retams its eggs till they have reached a my advanced stage of development. This figure is borrowed 



tssiz in 1848. I n the Ophiurans, also, the young of some species are 



drawin^ 



A Grass 



Quatrefa 



man 



and Krohn in MUll Arch, 



