}. \] . Jul 



M E M I R S 



OF THE 



AMERICAN ACADEMY 



\IlX 



ez. "T*^ 





I. 



On the Einhryohgy of Echinodenns. 

 By ALEXANDER AGASSIZ. 



Communicated February 2d, 1864. 



The following account of the embryology of a few of our Echinoderms, though by 

 no means complete, will fill several of the gaps hitherto existing in the knowledge of 

 the development of Echinoderms ; and in the hope that something may be added to 

 our understanding of the general plan of development of Echinoderms, it is here given 

 in its present condition, in order to show how far the plan of development is identical 

 in the different orders of Echinoderms. I shall take up in turn the Echinoids, Ophi- 

 urans, and Holothurians, and then compare these different larva) with what we know 

 already of the development of our common Starfish, to see how close the agreement of 

 the mode of formation of the young Echinoderm is in these four orders, and to satisfy 

 ourselves how true are the suggestions made at that time, on a very superficial ac-* 

 quaintance with any other Echinoderm larva except that of Asteracanthion, concerning 

 the function of many of the organs of these wonderful larvae. 



TOXOPNEUSTES DR015ACIIIEN8IS Ag. 



The larvae of our common Echinus resemble most closely, in some of their earlier 

 stages, those of Toxopneusies lividus Ag., figured by Miiller on Plates VI. and VII. of 

 his fourth Memoir.* Tlie figures which Miiller gives correspond with what I have 



• MuLLER, J. Ueber die Larvcii unci die Metamorphose der Echiiiodermen. Vierte Abliandlun-;. Ber- 

 lin, 1852. 



VOL. IX. 1 



