ASHFORD : ON THE DARTS OF BRITISH HELICID^. 167 



apply in great measure to the former. In both cases the sac is 

 free, that is, not fused to the vagina, and is a simple clavate or 

 subclavate pouch. 



Each of the two mucous glands divides into two branches, 

 and each of these again into either two or three others, but the 

 exceptions to this rule are very numerous. Examination of a 

 large series suggests a tendency in this organ to depart from a 

 system once purely binary, for instances of bifurcation twice 

 repeated are still common. Fig. 7 represents in their natural 

 size a pair of mucous glands thus disposed, while fig. 8 shows a 

 single gland in which the ramification is much less regular, and 

 the branches more numerous. In the arrangement most 

 frequently occurring, tliere are four branches in one group and 

 five in the other. Moquin-Tandon counted in one case a total 

 of 13 branches. I have never met with more than 11 nor less 

 than 5 in full-grown examples. Dr. Gray, in a short communi- 

 cation upon the subject to the Annals of Philosophy in 1825, 

 describes the mucous glands of H. nejnoralis as being " more 

 lobed " than in H. hortensis. On an average the reverse is the 

 case. They differ also in form. In H. hortensis the branches 

 are not cylindrical as in H. nemoralis, but irregularly tumid, 

 especially towards the extremities, and a somewhat medial 

 stricture is often noticeable, the portion below it being coloured 

 and the part above white. A monstrosity once came under my 

 notice, caused by the fusion of about 12 mm. of the two gland- 

 stalks into one thick stem bearing seven branches. 



The dart is invariably curved. The four blades start quite 

 ■abruptly a little above the expanded basal margin and therefrom 

 converge gradually and gracefully towards the point, a little 

 short of which they disappear. The greatest diameter is thus 

 at the lowest part of the blades (fig. 9). Each blade-margin 

 divides into two prominent flanges forming smooth obtusely- 

 angular channels or troughs (fig. 10a). The spaces between the 

 blades never exhibit the septa described under H. nemoralis. 



