332 MASON : VARIATION IN THE SHELLS OF THE MOLLUSCA. 



it has not yet attained to the dignity of distinct limbs, so that 

 many of the forms produced by reduplication, coalescence or 

 suppression are impossible. Again, so many of the group are 

 hermaphrodite, and therefore destitute of secondary sexual 

 characters, that the so-called gynandromorphs cannot be looked 

 for. 



Are there Hybrid MoUusca ? As far as I know this is a 

 question that has never been satisfactorily answered in the 

 affirmative, but the difficulty or impossibility of applying the 

 physiological test prevents any certain answer being given. 

 Among insects it has been found possible to artificially pair 

 nearly allied species, and so produce undoubted mules, and in 

 the vegetable kingdom, numerous florists' flowers, as is well 

 known, are thus produced. 



I do not know that any case of mimicry has been brought 

 forward among the mollusca. By mimicry I mean the protec- 

 tion acquired, as is especially seen among insects, by the 

 assumption of characters similar to those of other species which 

 are distasteful to the creatures which prey upon them, or to 

 inanimate objects like dry stick or parts of plants, some insects, 

 indeed, being quite indistinguishable when at rest upon a plants 

 from its own leaves and twigs. The only approach to this is 

 the change of colour occurring among the Cephalopods, due to 

 the more or less diffusion of the colour in the pigment cells, 

 according to the colour of the ground over which they are 

 swimming. It is quite true that certain specimens, as Mr. Melvill 

 states, of the Oimlum i/nplkaiuin, of Florida, are purple or 

 yellow, as they live among the Gorgonke of those colours, but 

 this may be due to the colour of the food. The majority of the 

 mollusca are so little dependent on locomotion for the supply 

 of food that we cannot expect to find varieties such as are 

 developed in other classes by an activity greater or less than the 

 average in the pursuit of prey. There is doubtless a wide field 

 open to anyone who will investigate the variations in the 

 animals themselves, but this is practically an untrodden field 



J.C , vii., Jan. 1894 



