Chap. II. RECAPITULATION. 45 



produces but one Starfish, and the whole of the larva is resorhed by the Starfish, not 

 an appendage being left out. Nor is it strictly a metamorphosis, as the changes 

 which take place are so gradual that at no time can the line of demarcation be 

 drawn between two stages with any degree of precision, as in Crustacea or Insects, 

 where the casting of an envelope marks distinctly different epochs. There is, however, 

 something in these successive phases of development which reminds us of the 

 metamorphoses of Insects. There is a sort of general similarity between this 

 process of resorption, and the growth and changes in the chrysalis of Lepidoptera, 

 ending in a butterfly. In the latter case, the chrysalis, though retaining its 

 character throughout the whole growth and development of the Insect, has an 

 earlier stage when it seems to be purely chrysalis, and a later one immediately 

 before the hatching of the perfect Insect, when the butterfly seems to be gaining 

 the ascendency, and the whole outline of its form may be seen through the chrysalis, 

 which now seems to be only its envelope. And yet the character of the develop- 

 ment, during its Brachiolaria stage, recalls vividly the phenomena of alternate 

 generations. It is, nevertheless, strictly echinodermoid, and whether we observe it in 

 the Ophiurans, the Sea-urchins, or the Holothurians and Crinoids, there seems no 

 doubt, from the observations of Miiller, Busch, Thompson, Krohn, and Agassiz, that it 

 is carried on according to one and the same plan in all the orders of the class, where 

 we have corresponding differences in their various modes of development; and with 

 reference to the separate existence of the larva and of the Echinoderm, urged by 

 other observers, I can only say that nothing of the kind has occurred in those 

 Echinoderms the changes of which I have traced, whether it be an Ophiuran, an 

 Echinus, a true Starfish, or a Holothurian. 



RECAPITULATION. 



I shall, in a few words, recapitulate the development of these Starfishes, in order 

 to be able more fully to compare my observations with those of previous writers, 

 and the reasons of the differences, when they exist. 



Changes of the Yolk. — The yolk separates, after fecundation, slightly from the 

 outer envelope. The segmentation takes place rapidly; as soon as the yolk has 

 divided into eight portions, they arrange themselves in such a manner as to enclose 

 the remaining space, which is more and more separated as the spheres increase in 

 number, until, finally, there is a complete envelope formed of spheres of segmentation. 



Scyphistonia, or pyriform Stage. — At the time the young escapes from the egg, it is 

 spherical, and the walls of the envelope are of the same thickness. One side becomes 

 thicker, the embryo flattening at this extremity, which is bent in so as to form a 

 slight cavity, in which fluids circulate. This cavity extends half-way the length of 



