226 



membrane between the rings. The respiratory system is con- 

 structed after the same type in both. Prof. Agassiz next pro- 

 ceeded to give a detailed description of the solid framework of the 

 Lobster. He showed that the terminal plate of the tail, which 

 is furnished with broad flat fins, is not a locomotive appendage 

 merely, but properly a ring of the body. The anterior pair of 

 these caudal locomotive organs, speaking morphologically, is the 

 penis, which shows some indications of divisions, like the joints of 

 the legs. In most Crustacea the second pair of claws is enlarged 

 so as to furnish instruments of defence. In the Lobsters, the claws 

 thus enlarged have been hitherto considered the first pair of 

 thoracic limbs; but on careful examination, Prof. Agassiz found 

 in advance of the second a very small pair, which had hitherto 

 been overlooked ; he therefore considers the last pair of jaw-legs, 

 as thoracic limbs properly belonging to the organs of locomotion. 

 In conclusion. Prof. Agassiz remarked that his analysis of the 

 component parts of each division of the Lobster showed that 

 the number three with its multiples is the fundamental number 

 upon which it is made up, and that this obtains for the chest as 

 well as the other regions of the body. The name of Deca- 

 jpods is therefore inappropriate for any group of Crustacea. 



Mr. Whitney said that in the Bruce Slate Quarry at Guilford, 

 Vt., the vertical strata are at one point broken abruptly, over 

 an area of only one hundred square feet. Prof. Hitchcock 

 had suggested that the fracture might have been caused by the 

 sudden impulse of a large mass of floating ice. During the past 

 summer he had seen a similar fracture at Lake Superior, at the 

 Jackson Forge. Here the slate strata are nearly vertical, bear- 

 ing nearly north and south. Over a small portion of the top of 

 the hill there is a fracture precisely like that at Guilford. The 

 strata have been carried forward as well as bent and crushed, as 

 if they had been swept along by the crushing force. The dis- 

 placed portion is imbedded in stratified drift, which is lodged in 

 the depression beyond the ledge. These appearances are 

 strongly corroborative of Prof Hitchcock's theory, that such 

 fractures are caused by the crushing action of icebergs. 



Prof. Hitchcock remarked that the suggestion was not original 

 with him, but he had borrowed it from Darwin, who attributed 

 similar fractures in the slate rocks of Great Britain to the action 

 of enormous icebergs floated up and down by the movements of 

 the ocean, and thus lodged on these rocks. 



