146 Royal Society. 



existence of another organ with which its presence alternates, and 

 which, in many fishes, assumes the form of a minute supplementary 

 gill, the vessels of which communicate, on the one hand, with the 

 systemic veins about the base of the cranium, and on the other, by 

 a single long trunk with the first branchial vein. 



Although the thyroid gland occupies various situations in dift'er- 

 ent animals, it always maintains an intimate relation with the vas- 

 cular supply of the brain, and is always so nourished as to be 

 capable of a greater or less nutrition according to the activity or 

 repose of that nervous centre. 



3. " On the Resolution of Numerical Equations." By Joseph Agar, 

 M.D., Fellow of the Royal College of Physicians. Communicated 

 by John Ayrton Paris, M.D., President of the College. 



The object of this paper, which is purely analytical, is to explain 

 a method of resolving numerical ecjuations with real coefficients, 

 which recommends itself by its simplicity and generality. 



4. " On the Reproduction of lost parts in Myriapoda and Insecta." 

 By George Newport, Esq., F.R.C.S., President of the Entomo- 

 logical Society of London, and Corresponding Member of the Phi- 

 lomathic Society of Paris. Communicated by P. M. Roget, M.D., 

 Sec. R.S. 



It has long been known that the limbs of Crustacea and Arach- 

 nida, accidentally lost or designedly removed, are, in course of time, 

 replaced by the growth of new limbs ; and the same power of re- 

 production has been stated to have been observed in the Phasmae, 

 insects which undergo neither metamorphosis nor any change of 

 habits. But whether such a power exists in those insects, such as 

 the Lepidoptera, which undergo a complete metamorphosis, changing 

 not only their form, but also their food and mode of life, in passing 

 from the larva to the adult state, has been considered as very doubt- 

 ful. The instances in which the reproduction of lost parts appeared 

 to have occurred in some of the Myriapoda, were attributed to im- 

 perfect or arrested development. With a view to determine these 

 unsettled points, the author commenced, in the summer of 1841 and 

 1842, a series of direct experiments on this subject in the Myri- 

 apoda; and in the present summer he has extended them to the 

 Lepidoptera. The results of his labours are given in the present 

 memoir. 



In some specimens of lulus, from which he had removed the an- 

 tennae and some of the legs, the lost organs were found to be com- 

 pletely reproduced after the next change of integument; differing 

 from the original organs only in their smaller size, and the incom- 

 plete development of some of their minuter parts. The same results 

 followed from similar experiments made on the Lithobris during the 

 earlier periods of its growth. One individual of this genus, which 

 had already acquired the tenth pair of legs, was by accident deprived 

 of the eighth, ninth and tenth pair ; at the next change of skin it 

 not only developed two additional pair of legs, but also reproduced 

 the three pair which had been lost. Some time after this it again 

 lost one of the legs of the twelfth pair ; a loss which was repaired 



