BY C. J. MARTIN AND FRANK TIDSWELL. 485 



The layer of smooth muscle fibres is no doulit lirought into 

 action to help to express the secretion when the animal "sti'ikes." 

 The large alveolar spaces as well as the duct serve as store-house 

 for this fluid. When the animal contracts its powerful gluteus 

 maximus and the other muscles at the back of the thigh, the gland 

 would be compressed to some extent. As, however, these muscles 

 must he constantly so contracted when the animal runs and 

 swims Avithout causing the discharge of the contents of the gland, 

 such muscular contraction cannot be considez'ed as the only cause 

 <.)perating. We think that the contraction of the thick panniculus, 

 which envelopes the leg in this region, is in all prol)ability the 

 principal agent concerned, and that the smooth muscle of the 

 capsule co-operates with it in effecting this end. The fact that 

 the muscle fibres of the gland itself are of the unstriped variety, 

 does not necessarily prevent them from being indirectl}^ under the 

 influence of the will. The pupil of the eye in mammals is provided 

 with muscle of the same unstriped character, which can be brought 

 into operation in associated action with certain voluntary muscles. 



As regards the duct proper, sections were made from a portion 

 al)out midway between the gland and spur. Most of these 

 (PI. XXIX. fig. 3) showed two channels (some, however, three and 

 others only one) embedded in white fibrous tissue. This duplica- 

 tion of the lumen of the duct, which was noted by Rudolphi,* 

 indicates that in the development of these specimens the 

 branching of the original invagination had occurred lower down than 

 is usual in such structures. In all cases the duct was single at 

 the lower end. The duct contains no muscular tissue whatever. 

 We haAe made serial sections from every region, including the 

 dilatation situated at its lowest end, without discovering any trace 

 of muscle. This seems to us the more remarkable as under 

 ordinary circumstances it is impossible, either in the living or 

 recently dead animal, by pressing on the gland to drive the 

 secretion through the spur. So that the animal must possess 

 some arrangement for obliterating the channel and so pi-eventing 

 undue waste of the seci-etion. 



* A'oliand. d. Berlm. Akad. 1820-21. Abtheil. i. p. '233-236. 



