Royal Society. 21 1 



heads: 1st, that of an animal produced from the egg in the form 

 which it is destined to retain through life, its only change consisting 

 in a series of moultings of the outer envelope, attended merely by an 

 increase of size, and not by the acquisition of new organs ; 2ndly, 

 when the animal, at its exclusion from the egg, exhibits the form which 

 it continues to possess, subject to a series of moultings, during several 

 of the last of which certain new organs are gradually developed ; and, 

 3rdly, when the form of the animal, at its exclusion from the egg, is 

 totally different from that under which it appears at the later periods 

 of its existence 3 such change of form taking place during two or three 

 of its general moultings, and consisting, not only in the variation of 

 the form of the body, but also in a complete change in the nutritive 

 and digestive systems, and in the acquisition of various new organs. 

 This last phenomenon peculiarly characterizes what is termed a meta- 

 morphosis. 



It is the received opinion among naturalists that the Crustacea do 

 not undergo metamorphoses, properly so called, and that the trans- 

 formations they exhibit consist merely in the periodical shedding of 

 the outer envelope. The object of the present paper is to establish 

 the correctness of this opinion, in opposition to that of Mr. J. V. 

 Thompson, who has laid claim to the discovery that the greater num- 

 ber of the animals belonging to the class Crustacea actually undergo 

 metamorphoses of a peculiar kind, and of a different character from 

 those of insects. Mr. Thompson's views are founded upon some cir- 

 cumstances which he has observed in certain animals of the genus 

 Zoea of Bosc, and which have been recorded by Professor Slabber, and 

 which led him to believe that, of these animals, some were the young 

 of the Cancer Pagurus, or common crab, and others the young of the 

 Astacus Pagurus, or common lobster j and these views are supposed 

 by him to be corroborated by the annual peregrinations of the land 

 crabs to the sea-side for the purpose of depositing their eggs, ren- 

 dered necessary by the aquatic habits and conformation of the young. 

 The author then proceeds to examine at length the arguments on 

 which Mr. Thompson has founded these opinions, and adduces his 

 reasons for concluding that they are erroneous, and that no excep- 

 tion occurs to the general law of development in the Crustacea, 

 namely, that they undergo no change of form sufficiently marked to 

 warrant the application to them of the term metamorphosis. 



u Memoranda relating to a Theory of Sound." By Paul Cooper, 

 Esq. Communicated by J. G. Children, Esq., Sec. R.S. 



The author, expressing his dissatisfaction with the commonly re- 

 ceived theory of the propagation of sonorous undulations by an elastic 

 medium, advances the hypothesis that each particle of an elastic body, 

 after receiving an impulse in a particular direction, and communi- 

 cating that impulse to the adjoining particle, instead of being thereby 

 brought to a state of rest, is carried back by its elasticity with a velo- 

 city which continues its motion beyond the point from which it origi- 

 nally set out, and is thrown into continual vibration, in a manner 

 analogous to the motion of a pendulum. He endeavours, on the prin- 

 ciple of a continual transfer of the state of each particle to the adja- 



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