196 Prof. Agassiz on the Echinodermata. 



has added some details upon the nervous system of this spe- 

 cies which had escaped the observation of M. Grube. 



M. J. Mliller has studied in great detail the organization, 

 considered comparatively, of the Pentacrinus Caput Medusce, 

 of which he has just procured an example, preserved in spirits 

 of wine. The publication of his memoir will form a most im- 

 portant addition to our knowledge of the anatomy of the 

 Echinodermata: unfortunately as yet an extract of it only 

 has appeared in the Bulletin of the Berlin Academy for April 

 1840; but so concise, and so rich in new facts, that it would 

 be necessary to quote it entire to give a just idea of its value. 

 So much of it as is already made public is of the highest in- 

 terest, M'hether considered anatomically or zoologically. M. 

 J. Miiller, in his description of the sohd parts of this animal, 

 rejecting the fanciful nomenclature first employed by Miller, 

 and subsequently by all those who have since Avritten upon 

 the Crinoide(S, proposes a far more simple terminology for its 

 complex frame-work. 



Many points of detail relating to the anatomy of the Echi- 

 nodermata have been investigated with equal success. M. 

 Krohn has published a very interesting memoir upon the 

 nervous system of the Echinidce and Holothuriada (Miiller's 

 Archiv, 1841, p. 1), which M. van Beneden has observed in 

 the Sea-urchins (Instit., No. 273, p. 96). Ehrenberg first dis- 

 covered the existence of eyes in the Asterice (Miiller's Archiv, 

 1834, p. 570), and described their connexion with the nerves 

 of the rays ; they may be very easily seen in many species, 

 even when in the dry state. Mr. Forbes subsequently pointed 

 them out in the Sea-urchins (Hist. Brit. Starf, p. 152), and I 

 have since observed them in many species. MM. Ehren- 

 berg (Miiller's Archiv, 1834, p. 580), de Siebold (ibid, 1836, 

 p. 291), Valentin (Repert., vol. ii. p. 26), and J. Miiller (Bui. 

 de I'Acad. de Berlin, 1840), have given detailed information 

 respecting the calcareous network of which the solid frame- 

 work [charpente solide) of the Echinodermata is composed. 

 For ray own part I have endeavoured to determine the laws 

 of the disposition and of the increase of the separate plates, 

 and their analogy in different families (Memoires de la Soc. 

 des Sc. Nat. de Neuchatel, tom. i. p. 2 — 6 and 7 — H), re- 

 specting which M. Philippi has offered certain objections 

 (Wiegmann's Archiv, 1837, vol. i. p. 194). M. Duvernoy 

 has communicated to tlie French Academy of Sciences his 

 ideas respecting the solid framework of these animals (Instit. 

 1837, No. 216, p. 208), to which he attributes an internal 

 skeleton, but peripherique (Sea-urchins), whilst he regards 



