PATELLA. 251 



into a mass of sex cells covering the connective basis. As 

 the gland grows in each season towards maturity it pushes 

 forwards, sometimes as far as the level of the oesophageal 

 pouches, and often extends across the median line towards 

 the right side (fig. 8). At the time of complete maturity 

 the ova are surrounded by a tough coat, which possesses 

 a micropylar opening. The ovum contains numerous 

 yolk spherules (fig. 33b). The sperms (figs. 34) are very 

 minute and consist of head and tail as usual. 



The gonad expels its products by rupture into the 

 cavity of the right kidney, and they thus make their way 

 /to the exterior. The gland seems peculiarly liable to 

 overgrowth, and, among specimens collected in autumn 

 on the Welsh coast, various ruptures can frequently be 

 noticed, sometimes between the shell muscle and the 

 foot, sometimes above the shell muscle, though this latter 

 does not seem to be of any advantage for the expulsion 

 of sex products. The season of sexual maturity is the 

 autumn; Boutan finds it to be about September at Boscoff ; 

 at Aberystwyth we think it is somewhat later. A few 

 limpets have been found by Gemmill with male and 

 female regions in the gonad, and he also notes that the 

 percentage of the two sexes do not depend on tidal level. 



Though the gonad is situated on the animal's left side 

 it must not, therefore, be supposed to be the (post- 

 torsional) left member of an ancestral pair, for there have 

 been such changes in connection with the consolidation 

 of the hump that the present position cannot be taken as 

 a guide. The evidence rather points to the view that we 

 have here the (post-torsional) right member of the 

 ancestral pair, f or : — 



(1) In all other classes of Gastropods the (post-torsional) 

 right gonad, and, in Cephalopods, the one corresponding 

 to this (i.e., the left), is the one which survives. 



