200 ASHFORD : ON THE DARTS OF BRITISH HELICID^E. 



terminals to each gland ; in the case of juniors the branches 

 are shorter and fewer, from which we may fairly conclude that 

 the process of ramification as well as increase of length goes on 

 pari passu, with the growth of the animal. Figures 1 1 and 1 2 

 represent the two extremes that have come under my own 

 observation, one with only 14 terminals (animal adult, dart 

 perfect), the other with the unusual number of 46. Note in 

 fig. 1 2 two or three examples of terminal budding, and com- 

 pare with a similar case (fig. 2) in H. arbustoriim. 



The curvature of the dart (fig. 13) is somewhat variable 

 and sometimes nearly confined to the apical half. Capt. Thos. 

 Brown, in his ' Illustrations of Land and Freshwater Con- 

 chology,' represents it nearly straight, but I have never found it 

 so. A little above the point where the base begins to enlarge, 

 start the four simple blades, increasing in breadth more rapidly 

 and converging towards the point more gradually than in H. 

 nemoralis, so that their greatest width is attained below the 

 middle of their extent. If the dart be snapped near the middle 

 the four blades will usually be found equally sahent as seen in 

 the section (fig. 13), if broken near the point the two pairs will 

 as commonly be found unequal owing to one pair feathering 

 off sooner than the other pair. A very abnormal form, almost 

 amounting to a monstrosity, is shewn in fig. 15, where the 

 principal blades — viz., those in the plane of curvature — have 

 been unduly developed apparently at the expense of the side 

 blades. Fig. 14 shows a real case of malformation, the result 

 probably of injury during growth. 



The darts of H. aspersa and H. nemoralis resemble each 

 other in the general aspect of the base, in the singular combina- 

 tion of brittleness and softness when moist from the sac, and 

 in the character and disposition of the crescentic films between 

 the blades. 



Dr. Martin Lister (1694) mentions and figures the dart of 

 this species. Montagu (1805) justly ridicules the notion preva- 

 lent before his time, that these weapons were used as missiles. 



J.C, iv., July, 1S84. 



