548 GEORGINA SWEET. 



it [10, pp. 22, 23], that " it is not visible exteriorly/' has " no 

 bony orbit/' and " consists of a small circular pigment spot " 

 — and three years later, a longer reference was made to it 

 [11, pp. 159, 180] giving its position in the head and its 

 general characteristics, concerning which Dr. Stirling writes : 

 — "I cannot be absolutely certain of its relations, or of the 

 morphological value of its constituent parts." As the result 

 of careful study of some seven or eight heads, I am able not 

 ouly to corroboi'ate Dr. Stirling's observations so far as they 

 go, but also to record a quantity of additional information 

 which will, I think, make clear the homologies of this very 

 interesting relic, forming at the same time a striking study in 

 degeneration and convergence. Considerable variations are 

 met with in the different points of structure, as might be 

 expected in a degenerate organ, and the following description 

 takes note of the more important of these variations, while 

 at the same time, it is based on the most constant featui-es. 

 It is a matter for regret that the embryo of this animal has 

 not yet been obtained, as no doubt considerable light would 

 be thrown on the degeneration of the eye by the study 

 of its early stages. 



In seeking to trace the homologies of the eye of Noto- 

 ryctes typhlops, in the following account of its structure, I 

 have refrained from making comparisons or contrasts with 

 other forms, except in such cases as seem of assistance or 

 special interest. 



Position. 



The whole eye, with its gland, the nerve, blood-vessels, 

 muscles, etc., is situated at a distance of 13 mm. from the 

 anterior end of the snout, deeply seated beneath the tem- 

 poralis muscle, and often covered with a mass of connective 

 tissue (contrast Typhlops, where the ordinary subcutaneous 

 tissue is thinner [6, p. 119], and compare Siphonops [6, 

 p. 105] and Typhlomolge [2, p. 51]). In addition to this 

 the dermis and epidermis always pass over this region un- 

 altered in general structure and thickness, in contrast to Pro- 



