DEX'ELOPiAlENT OF A GASTROPOD 969 



of the modern F . caricum first make their appearance. In a more 

 advanced type, F. tritonis (Fig. 256, /), the characteristic round 

 "maximum" type of whorl has become restricted to a few earher 

 whorls, the adult whorl being marked by the spinous "caricum" type 

 of whorl. Different individuals show progressive encroachment of 

 the "caricum" type on the "maximum" type, until the latter has 

 been completely superseded, the spines then following immediately 

 upon the tubercles ; and, in still more advanced forms, becoming 

 telescoped with them. This is the character of the modern type, 

 where the tubercles pass imperceptibly into the earliest spines. 

 It is thus only by the consideration of the intermediate Tertiary 



Gl ' I ^ I ^ I ^ I ^ 1 i 



Fig. 257. Diagram illustrating the development of the Fulgur series. 



Stage I is the protoconch which persists throughout. 



Stage 2 is the smooth shell stage which in the primitive species A forms 

 the adult, but in B is shortened. 



Stage 3 is the ribbed stage, which is wanting in A, but in a somewhat more 

 advanced species B is well developed in the adult. 



Stage 4 is characterized by an angular whorl, the ribs still continuing. It is 

 the adult character of species C, in which stages 2 and 3 are condensed. 



Stage 5 is the tubercled stage characteristic of the adult of F. fusiformis. 



Stage 6 is the smooth round-shelled stage found in the old age of species D 

 and the adult of E. 



Stage 7 {F. maximum) shows the caricum spines well developed in species 

 F while in species G the modern F. caricum, Stage 6, has been eliminated and 

 Stage 7 follows directly upon the tubercles (Stage 5). 



types that the true history of the development of the Fulgurs is 

 learned, the individual life history of the modern F. caricum being 

 an abbreviated and incomplete recapitulation of the history of its 

 race. Here acceleration has been so pronounced as actually to 

 eliminate certain stages in the sequence of development. The pre- 



