68 THE CONSTITUTION OP THE GASTROPOD PROTOCONCH, 



is an inhabitant of deep waters, it is large. Similar phe- 

 nomena have been recorded for Murex tribulus and Sipho 

 gracilis. Boettger has collected these together under the 

 name of "Heterostylie," and has expressed the opinion that: 

 "It seems indeed that the embryos of a single genus are able 

 to undergo a kind of adaptation, and that this differential 

 character, far from recalling an ancestral form, appears as an 

 accommodation entirely secondary." 



That the variation is due to environmental conditions, 

 seems at least exceedingly probable, in view of the phenome- 

 non presented in I'ahemonetes varinns. In this case, the 

 primary factor responsible for the variation was undoubtedly 

 the alteration in the concentration of the salts in the water. 

 This may have acted only through the resultant change in 

 osmotic pressure, but more probably through the change in 

 concentration and relative proportion of the individual salts 

 (see Loeb, 36, 37; Ringer, 43; and W. A. Osborne, 39, 40); 

 and also, perhaps, by the change in foodstuffs, for the change 

 in saline contents of the water would exterminate some mem- 

 bers of the related fauna and flora, and allow of their replace- 

 ment by new forms. 



I would explain the large Gastropod Protoconch as result- 

 ing from a modification of the mode of production, induced 

 by some new condition in the environment, and leading to an 

 increase in the size of the ovum and perhaps also, in some 

 cases, an increase in the intra-capsular nutrient material. 

 The former would determine a large thimble-shaped nucleus, 

 and the latter permit a maintenance of the rapid growth of 

 the larva whilst still within the egg-capsule. In the deep 

 water forms it is probable that the Velic/cr stage is passed 

 within the egg-capsule. As causative factors in the case of 

 Fusus hifrons, etc., we may point to the difference in pressure, 

 and the attendant difference in saline contents of the water. 



Such an explanation as the above is not available for such 

 bizarre forms of the protoconch as, for instance, the Siniisi- 

 qera; but, in these, it is probable that a study of the living 



