278 MB. A. THOMSON'S REPORT OX THE IXSECT-HOUSE. [Mar. 28, 



the elements not directly related to the two digits (III & TV) which 

 were alone normally functional were in a backwardly developed 

 state, as though they had been subjected to an arrest in growth. 

 This was especially the case with the intermedium (i) and centrale 

 (c). That the departures from the normal here met with admit of 

 ready explanation on purely physiological grounds is sufficiently 

 clear ; but the case is none the less interesting morphologically, 

 as in those Urodeles possessed of numerically reduced digits 

 both the reduction and fusion of all parts involved are invariably 

 effected in a progressive manner from the post-axial or outer 

 side inwards ^ and accompanied by a diminution in length of the 

 outermost digit. 



Numerical variation of the digits is most marked among the 

 Amphiumidas of all living Urodeles, the individual variations being 

 such as to have led Cope to the conchisiovr that Amphiuma tridactyla 

 is but a variety of A. means, the digits of the species ranging from 

 1 to 3 in number in both fore and hind limbs. These facts, taken 

 in conjunction with the recent discovery of a fleetiug vestige of the 

 pelvic member in one alone among a series of larvse of Ichfhi/ojyJiis 

 gluthiosa examined by the cousins Sarasin ^, show that individual 

 variations of the kind herein recorded may realize (admittedly in a 

 perliaps distorted form at times) the steps by which the reduction 

 and loss of limbs have been effected in allied genera and species. 



March 28, 1893. 



Sir W. H. Flower, K.C.B., LL.D., F.E.S., President, in the 



Chair. 



Mr. Arthur Thomson, the Head Keeper, exhibited a series of 

 Insects reared in the Insect-house iu the Society's Gardens during 

 the past year, and read the following Eeport on the subject: — 



Heport on the Insect-Jiouse for 1892. 



Examples of the following species of Insects have been exhibited 

 in the Insect-house during the past season : — 



Sill'-producing Bomhyces and their Allies. 



Indian. 



Attacus atlas. Anthera^a mylitta. 



cynthia. Actios selene. 



])crnyi. Cricida trifenestrata . 



roylei. 



^ Cf. Baur, ' Beitr. z. Morphogenie d. Carpus uud Tarsus.' Tli. I. Batrachia. 

 Jena. 1888. 



- Proc. Amer. Phil. Soc. 1886, p. 526. Cf. also Hay, Amer. Nat. 1888, 

 p. 315 ; and Cope, Batrachia of N. America, p. 218. 



^ Ergebnisse Naturwiss. Forscbung. auf Cejlou, Bd. ii. Hft. 2, p. 22. AA'ies- 

 baden, 1887 



