Prof. Agassiz on the Echinodermata. 297 



but I am onl)- acquainted with his researches from extracts 

 (Wiegm. Archiv, 1838, vol. ii. p. 333). 



The history of the development of the Echinodermata is 

 enriched with many important facts. M. Sars has made 

 known the changes Avhich the Asterias sanguinolenta of 

 Mliller undergoes during the early stages of its existence. 



Mr. Thompson of Cork, twelve years after having described 

 his Pentacrinus europceus, published a second memoir on 

 this animal, in Avhich he regards it as the young state of the 

 Comatula rosacea. This opinion has been fully confirmed by 

 Messrs. Forbes, Thompson of Belfast, and Ball, who have 

 seen the living Pentacrbms europceus detach itself from its 

 stalk, and swim freely in the form of a small Comatula. The 

 information given by Mr. Forbes regarding the development 

 of this Comatula is highly curious. 



M. de Siebold has indicated the existence of the vesicle 

 and the germinal spot in all the Asterue which he examined 

 (Midi. Archiv, 1836, p. 297). M. J. Midler has also described 

 the vesicle and germinal spot of the Comatuke and Ophiurce. 

 M. Peters (Miill. Archiv, 1840, p. 143) announces that the 

 Sea-urchins have the sexes distinct. They do not differ ex- 

 ternally it is true ; the sexual organs in both males and 

 females have the same appearance ; but in the females of 

 Echinus purpureus and E. Mela the sexual glands are red, 

 and contain ova where the vitellus and germinal vesicle are 

 to be distinguished, whilst in the males these are white, and 

 only filled with spermatozoa. MM. Valentin and R. Wagner 

 have likewise noticed a distinction of sexes amongst the Ho- 

 lothurice, and M. Rathke among the Asterice. M. J. Mliller, 

 moreover, observes that it is probal)ly the same in the Cri- 

 noidece, or at least in the Comatulce (Miill. Archiv, 1840, p. 144). 

 MM. Valentin and Miescher have observed spermatozoa in 

 the Spatarigus purpureits (Repert. de Valentin, 1840, p. 301). 

 M. Milne Edwards has confirmed these facts by additional 

 observations. 



In a special memoir inserted in Wiegm. Archiv. for 1837 

 (vol. i. p. 241), M. Philippi has described two monstrosities 

 in the genera Echinus and Spatangus. MM. H. de Meyer 

 and Agassiz have also made known various monstrosities ile- 

 pending both upon deficiency and excess. 



Many lengthy memoirs have appeai'cd upon the fossil 

 Echinodermata, and a large number of species will be found 

 described in a variety of general works upon geolog}' and 

 palaeontology. But these works are v.anting still in agreement, 

 most of the authors differing in opinion as to the limits which 

 should be assigned to genera. The genera which have been 



4nn,&iMa(/,N.Hist. Vol,i\. X 



