141 



mask ; when regarded in profile, the appearance is equally striking. 

 A framed picture, hung against a wall, appears as if imbedded in a 

 cavity made in the wall. An object placed before the wall of a room 

 appears behind the wall, and as if an aperture of the proper dimen- 

 sions had been made to allow it to be seen ; if the object be illumi- 

 nated by a candle, its shadow appears as far before the object as it 

 actually is behind it. 



The communication concludes with a variety of details relating to 

 the conditions on which these phenomena depend, and with a de- 

 scription of some other methods of producing the pseudoscopic 

 appearances. 



January 15, 1852. 

 COLONEL SABINE, V.P., and Treas., in the Chair. 



A paper was read, entitled, " On the Development of the Duct- 

 less Glands of the Chick." By Henry Gray, Demonstrator of Ana- 

 tomy at St. George's Hospital. Communicated by W. Bowman, Esq., 

 F.R.S. Received November 12, 1851. 



In this paper the author has demonstrated the evolution of the 

 spleen, supra-renal and thyroid glands, nnd the tissues of which 

 each is composed, in order to show the place that may be assigned 

 to each in a classification of the glands. 



The spleen is shown to arise between the 4th and 5th days, in a 

 fold of membrane \vhich connects the intestinal canal to the spine 

 (the " intestinal lamina"), as a small whitish mass of blastema, per- 

 fectly distinct from both the stomach and pancreas. This fold 

 serves to retain it and the pancreas in connection with the intestine. 

 This separation of the spleen from the pancreas is more distinct at 

 an early period of its evolution than later, as the increased growth 

 of both organs causes them to approximate more closely, but not 

 more intimately with one another ; hence probably the statement of 

 Arnold, that the spleen arises from the pancreas. With the increase 

 in the growth of the organ and the surrounding parts, it gradually 

 attains the position that it occupies in the full-grown bird, in more 

 immediate proximity with the stomach ; hence probably the state- 

 ment of Bischoff, that it ayises from the stomach. Later, when its 

 vessels are formed, the membrane in which it was developed is 

 almost completely absorbed. 



The author then considers the development of the tissues of the 

 spleen, which clearly establishes, not only the glandular nature of the 

 organ itself, but the great similarity it bears with the supra-renal 

 and thyroid glands. 



The external capsule and the trabecular tissue of the spleen are 

 both developed between the 8th and 9th days, the former in the 

 form of a thin membrane composed of nucleated fibres, the latter 

 consisting of similar fibres, which intersect the organ at first sparingly, 

 and afterwards in greater quantity. The development of the blood- 



