No. 490] 



ORTHOGENETIC VARIATION 



627 



Sycotypm caiialirulafii.^- tlu> size of the initial whorl is deteniiiiied 



fact the whole i>rotocoiich is foniicd aiul ihe aiiiiiial lias hcuun the 

 buildinj? of the eoiH-h l.efoiv it he.-onie. fivr Tlir ^aiii.' ihiii- is 

 true of Fasciolaria (/ir/a,tt(V an.l linrmnnn iunhthn,, ..eeMu.lies 

 ]I. p. To what extent tin. intraca,.M.Iar . I.-n rlnpn.ent is 



carried on in the species of Fusus and Mnrex cited, 1 hav(> not 

 been able to ascertain, l)iit it is most probably the case that the 

 protoconch stage is far advanced if not completed before the animal 

 l)ccomes free. The size of the initial whorl of the protoconch is 

 then probably to be rt^uarded as an expression of the size of the 

 embryo, its rapidity of orowth during the period of formation of 

 the hyaline i)riinitive shell, and the size it has reached before the 

 deposition of the calcareous matter begins. The size of the yolk 

 of the eggs, i. e., the initial food supply may, in turn, l)e con- 

 sidered as at least a partial factor influencing this ratt> of growth. 

 The factors advocated by Boettger are thus s^Moiuhiry factors 

 which may or may not determine survival. IMuw may indeed 

 hav(^ no sioiiificaiu'e whatever, for swollen initial whorls are found 

 in Fiisiis coins which ii\cs in from 10 to L*0 fathoms and F. mamora- 

 ius which li\ (^s in even shallower water. Among the Volutes, too, 

 whicli are conijiaratively shallow water forms, species like V. 

 musica have a minute apical whorl while V . rupestri^ Graelin, 

 ])roi)ablv belonging to a separate line of development, has a 

 large initi;d whorl. The initial whorl of the shallow water Fulgurs, 

 is much lamer than tliat of many decj) w ater species of other genera. 



Aside from the si/e of the initial wliorl of the protoconch, its 

 ol)li(iuity to the axis of coiling of the other whorls is a significant 



that is fusoid shells, and can be tra(ed back to the beginning of 

 this canal. If the initial eniar-ina(i..n. how.-vcr, forms some dis- 

 tance from the utnbilicus towani the periphery of the whorl, the 

 later whorls will coil on a different plane from tl.,- first, wliich is 

 often partiallN embraced bx or become- -Mnk.--: inm the Me.m<l 

 wliorl (Fig. In. Thi.t.irly rotation of the lir.i w horl . . „enrring 



characters itduM-eiU in the embrvo — at any rate it is difficult to 

 conceive how it can be a product of enviroiuneiUal influence on the 



