On the. Systematic Relations of Fishes. 155 



depends. When life no longer exists, then the acids mix with the 

 bases, and the coloured substances spread through the tissues. 

 The simple fact of the death of the protoplasm would there- 

 fore suffice, according to M. Prilleux, to explain all the pro- 

 perties of the frozen cells. 



As to the sheets of ice which are often seen during the 

 winter at the surface of stems or beneath the epidermis, these 

 originate, according to the same author *, from the water of 

 constitution of the membranes. Each molecule retains around 

 it, by the forces of attraction with which it is endoAvcd, a 

 liquid layer of a certain thickness ; under the influence of cold, 

 the force of attraction diminishes, and a part of the liquid flows 

 away and becomes frozen at the surface. 



[To be continued.] 



XIX. — Ohservations on the Systematic Relations of the Fishes. 

 (Abstract). By Prof. Edward D. CoPEf. 



I. Preliminary. 



The system of fishes, as at present adopted in America, is 

 the result of the labours of many naturalists, but chiefly of 

 Cuvier, Agassiz, Miiller, and Gill. Without going into the 

 history of the subject at present, it will be proper to point out 

 the principal modifications of Cuvier's system introduced by 

 his three successors. The orders of Cuvier were : — the Chon- 

 dropterygii, Malacopterygii, Acanthopterygii, Plectognathi, 

 and Lophobranchii. 



Professor Agassiz, under the name of Placoids, adopted the first 

 division ; the second he called the Cycloids, the third Ctenoids, 

 and then created a fourth order under the name of Ganoids, 

 which should embrace a portion of Cuvier's Chondropteiygii 

 (the Sturgeons), a portion of the Malacopterygii Abdominales 

 (the Bony Gars &c.) and the two last orders of Cuvier. Pro- 

 fessor Miiller, following with a still more complete anatomical 

 investigation, especially into the soft parts, discerned three 

 subclasses in Cuvier's Chondrostomi, which he named the 

 Leptocardii (Lancelet), Dermopteri (Lamprey &c.), and the 

 Selachii (Sharks &c.). In the then recently discovered Lepi- 

 dosiren he saw a fourth subclass, Dipnoi. 



Having instituted an investigation of Agassiz's Ganoid 

 order, in an able memoir he purged it of the Plectognath and 



* Bull. Soc. Botan. de France, 18G9, xvi. p. 140. 



t From the Association Number of the ' Anu'vican Naturalist.' Com- 

 municated bv the Author. 



11* 



