566 GEORGINA SWEET. 



sometimes in Notoryctes, remains in the less degenerate 

 forms as an indication of the path along which the conjunc- 

 tival sac was drawn inwards by the retreating eye. This 

 duct doubtless, as now in Talpa and Scalops, formed for 

 some time a last direct communication with the exterior. 

 This later on was lost, since evidently it was not of much 

 use to the animal, the sole remaining escape for the secretion 

 of the gland then being through the nasal duct into the nose. 

 The action of the muscular layer round the conjunctival sac, 

 as also that of the muscle bands which are attached to the 

 conical capsule, would be, by their contraction, to increase 

 the pressure on the conjunctival sac, directly and indirectly. 

 Their common innervation with the gland alveoli also 

 suggests that possibly efferent motor fibres maybe associated 

 with the efferent secretory fibres of the latter. The gland 

 must have now a considerable functional value, since, with 

 increasing degeneration of the eye and closing of the direct 

 passage to the exterior, the gland has increased in size. 



Presumably the present function of the secretion is — (1) 

 to keep the snout and nasal cavity moist, and (2) chiefly, to 

 hinder the entrance or accumulation of particles of sand in 

 the nasal cavity when burrowing, as this animal does so 

 rapidly in the fine sand in which it lives. 



Indeed, this cavity is often so full of coagulated secretion 

 that at first, in sections, no cavity at all can be found. 



The least degenerate of the eyes which I have been able to 

 examine is that in fig. 1, in which the gland is small, the 

 blind duct of the skin much longer, larger, and more definite, 

 while the appearance of the nerve-fibres is absent in every 

 other case — and there is no doubt whatever that, as the 

 eye becomes more degenerate, so the gland increases in size 

 and importance. 



Conclusions. 



Eigenmann [1, p. 546] remarks: — "It must be apparent 

 that an experiment on a vast scale has been conducted by 

 nature, leaving us but to read the results. Moreover, the 



