1883.] NATURAL SCIENCES OF PHILADELPHIA. 197 



process, which was described to the Academy, in the course of 

 which it lost one foot and two entire legs. This summer again, 

 during the latter part of August, the animal moulted ; the moult 

 as exhibited is a perfect cast of the large spider — skin, spines, 

 claws, the most delicate hairs all showing, and their corresponding 

 originals appearing bright and clean upon the spider. The moult- 

 ing occurred during Dr. McCook's absence, but was just finished 

 when he returned. When the cast-off skin was removed it showed, 

 as might be supposed, the dissevered members to be lacking. 

 But on looking at the spider itself, it was seen that new limbs 

 had appeared, perfect in shape but somewhat smaller than the cor- 

 responding ones on the opposite side of the body. The dissevered 

 foot was also restored. The loss of the opportunity to see the 

 manner in which the legs were restored during moult was greatly 

 regretted ; but we have some clue from the careful and interesting 

 studies of Mr. Blackwall. Several spiders whose members had 

 been previously amputated, were killed and dissected immediately 

 before moulting. In one of these the leg which was reproduced 

 was found to have its tarsal and metatarsal joints folded in the 

 undetached half of the integument of the old tibia. Another like 

 experiment was made with an example of Tegenaina civilis. The 

 reproduced leg was found complete in its organization, although 

 an inch in length, and was curiously folded in the integument of 

 the old coxa, which measured only one-twenty-fourth of an inch 

 in length. Dr. McCook's tarantula had lost both legs close up 

 to the coxae, and in the moult tlie hard skin formed upon the 

 amputated trunks was wholly unbroken, showing that the skin 

 had been cast before the new leg appeared. We risk nothing in 

 inferring that, as in the case of Blackwall's Tegenaria, the rudi- 

 mentary- legs were folded up within the coxae, and appeared at 

 once alter the moulting, rapidly filling out in^ manner somewhat 

 analogous to the expansion of the wings in insects after emerging. 



Messrs. Henry F. Clagliorn and Emanuele Fronani were elected 

 members. 



October 2. 

 Mr. Thos. Meehan, Vice-President, in the chair. 

 Twenty-eight persons present. 

 The death of Charles Magarge, a member, was announced. 



The Synchronism of Geological Formations. — Professor Angelo 

 Heilprin, referring to one of tlie many vexed problems which from 

 time to time engross the attention of geologists and naturalists, 

 namely, the contemporaneity of geological formations, stated that 

 the order of deposit of the various formations, from the oldest to 

 the newest, was constant the world over, and that nowhere, except 



