TAYLOR : LIFE HISTORY OF HELIX ASPERSA, 105 



"mucous gland." These are much ramified, offering about 

 25 branches in each bundle, but the number is so variable that 

 scarcely two individuals can be found agreeing in this respect. 

 H. pomatia is the only British species which surpasses H. 

 aspersa in the number of these curious coeca. 



Dart single ; shaft calcareous, opaque, white, curved, 

 more or less tubular, points at the free end, expanding into a 

 somewhat conical semi-calcareous base. Blades four, symmetri- 

 cally arranged, semi-transparent, simple-edged, disappearing 

 very gradually towards the point, somewhat more abruptly 

 towards the base which they do not reach, generally connected 

 with each other by more or less numerous (4 — 12) thin, trans- 

 parent, lunular, inclined, transverse plaits, like dried mucus 

 (which perhaps they are). Length 8 — 10 mm. 



The dart of H. aspersa belongs to a type whose character- 

 istics are shared by only one other British species, viz., H. 

 nemoralis (proper). Examination of a number of specimens 

 leads to the conclusion that the blades are the last parts formed 

 in the course of growth, but they invariably remain simple- 

 edged. Montagu is not so exact as usual when he describes 

 the dart of the species as " somewhat triangular," and Dr. Gray 

 is misleading when he calls it "exactly square with four sharp 

 angles." Lister's figure is poor, but probably represents faith- 

 fully the image in a microscope of that day. The possession of 

 the weapon is not essential for the proper union of two individ- 

 uals, for they sometimes unite before the dart has even com- 

 menced its formation. The statement is incorrect that H. 

 aspersa is provided with its spiculum only during the spring 

 pairing-time. Those which escape its loss during that period 

 retain the weapon throughout the autumn and succeeding 

 hibernation. When first dissected the dart of H. aspersa is 

 soft and flexible but it soon hardens with exposure to the air. 



