OF ARTS AND SCIENCES: APRIL 14, 18G3. Ill 



what I have been able to see of the development of our Cribrella, 

 I should think it highly probable that the peduncle is homologous to 

 the brachiolar appendages of the Brachiolaria. I would also suggest 

 that the two modes of development, the viviparous and plutean of the 

 Ophiurans, and the auricularian and the other mode of growth of the 

 Holothurians, do not differ in any other way, and that future investi- 

 gations will show that in all these cases the young Echinoderm is de- 

 veloped from the water-tubes, whether it is a nomadic or plutean 

 mode of development, as I shall call it, or a sedentary mode of develop- 

 ment, as we may call the second, where the eggs are carried about by 

 the parent till the young Echinoderm has passed through the greater 

 part of its development. 



The younger stages of the larva of the Echinus drohachiensis do not 

 differ, in their general features, from the mode of development of the 

 star-fishes. We have the same water bodies formed as diverticula from 

 the digestive cavity, the same differentiation of the digestive cavity 

 into an alimentary canal, a stomach, and an oesophagus. This differ- 

 entiation only takes place at an earlier period than in the star-fish, be- 

 fore the mouth is formed. However, there is nothing in the earlier 

 stages of development of the Sea-urchin which is not applicable as 

 well to the Brachiolaria. 



Figs. 1-9. — Asferacantkioti herylinus. 



Fig. 1 . Egg of Asteracanthion herylinus Ag., surrounded by spermatic particles 

 during artificial fecundation. 



Fig. 2. The yolk has divided into two segments. 



Fig. 3. The yolk has divided into eight spheres. We can already see at this 

 early stage the tendency of the peripheric arrangement of the spheres to 

 form an outer shell. 



Fig. 4. An embryo hatched from the egg a few hours, showing the diflference 

 in the thickness of the walls at the two poles (a). 



Fig. 5. The same as Fig. 4, somewhat more advanced ; a depression appears 

 at the pole («) where the thickening of the walls is found. This is the first 

 appearance of a mouth. 



Fig. 6. An embryo somewhat more advanced, in which this depression has 

 assumed the shape of a long digestive cavity (d), in which the opening (a) 

 performs at the same time the functions of anus and mouth. 



Fig. 7. The extremity of the digestive cavity at the time of formation of the 

 water system, at the moment when the two water-tubes (w, lo) are about 

 to separate from the digestive cavity {d), from which they arose as diverti- 

 cula ; they are still united in this figure. 



