280 MERISTIC VARIATION. [part I. 



414. Triopa clavigera (a Nudibranch): adult of the usual size, 

 having the lamellar rhinophore of the right side formed of three 

 branches, of which the two anterior were lamellar, borne on a 

 common peduncle, and the posterior was simple, of regular shape 

 and probably representing the normal rhinophore of the right side. 

 The rhinophore of the left side was normal. Ibid., S. 3, XXVIII. p. 131. 



415. Physa acuta: right tentacle bifid, left normal. Moquin- 

 Taxdox, Hist. not. des Moll. terr. et fluv. de France, I. p. 322, PL 

 xxxn. fig. 15. 



416. Helix kermorvani : a second eye present, close to, but 

 separate from the normal eye (Fig. 74, III.) on the left tentacle. 

 Ibid., PL xi. fig. 10. 



417_ Clausilia bidens : supernumerary eye on the right tentacle 



' as shewn in Fig. 74, IV. Ibid., PL xxm. fig. 24. 

 41 $ Littorina : supernumerary eye on one tentacle. Pelsexeer, 

 Ann. Soc. beige de microscojne, XVI., 1891. 



In examining large numbers of Pecten of several species, Mr Bkindley 

 occasionally found one of the eyes imperfectly divided into two, the division 

 being at right angles to the mantle-edge. 



Eyes of Ixsects. 1 



The following are examples of supernumerary eyes in Insects. 

 They are mentioned as examples of the development of tissues of 

 the same nature as those of the normal eye in abnormal situations. 

 All the cases known to me occur in Coleoptera. 



419. Toxotus ( = Pachyta) 4 — maculatus: a normal female. On 

 the vertex of the margin of the right eye and abutting against it 

 is a small third eye. This third eye is round-oblong in shape. It 

 is separated from the large eye only by the outermost margin of 

 the eye, and though it is more convex than the latter there is 

 nevertheless a considerable depression between the upper surfaces 

 of the two eyes. This supernumerary eye is of a brighter colour 

 than the normal eye, being brownish-yellow, while the latter is of 

 a pitchy black. It is facetted in the same way as the normal eye 

 is. Letzxer, K., Jahresb. d. Schles. Gesell.fur vaterl. Cidtur., 1881, 

 p. 355. 



420. Calathus fuscus : having a third eye. On the left side of the 

 vertex was placed a supernumerary eye. This structure was 

 smaller and less projecting than the normal eye and was separated 

 from it by the usual groove. It did not appear to be a part of the 

 normal eye which had separated from it, for the normal eyes of 

 the left and right sides were exactly alike. The integument of 

 the head was slightly wrinkled around the supernumerary eye. 

 de la Brulerie, P., Ann. de la Soc. Ent. de France, S. 5, v., 1875, 

 p. 426, note. 



421. Vesperus luridus $ : head abnormal and bearing a third 



1 For cases of eyes compounded in the middle line (Bees), see evidence as to 

 Bilateral Series. 



