1909.] NATURAL SCIENCES OF PHILADELPHIA. 371 



tive morphology of F. canaliculatum and F. carica are furnished 



by a study of the male reproductive organ. 



In the former species the penis is turned 



backward and folded (fig. 1). It likewise 



retains the same width at the distal end as 



at the proximal, while in addition the terminal 



process is relatively large. In F. carica, on 



the other hand, the organ tapers gradually 



from the proximal to the distal end and the 



terminal process is very small (fig. 3). The 



penis though turned backward is not folded 



at the turn as in F. canaliculatum. Gmelin. Diagram 



Influence of the Soft Parts on Shell Form and showing the normal 



male reproductive 

 Sculpture. — No one, of course, denies that all organ. 



the features of the gastropod shell, its form, 



size and ornamentation, are the result of changes in the lime-secreting 

 soft parts. A shoulder keel, for instance, is caused by a permanent 

 angle, while a spine represents the effect of a temporary elevation 

 of the mantle. What is it though which produces this temporary 

 bulging of the mantle edge? What is the physiological meaning of 

 the spine? This is a question which has never yet been satisfactorily 

 answered in spite of many ingenious suggestions. One view, often 

 expressed, holds that the spines represent an activity of the mantle 

 edge which is manifested at recurrent reproductive periods. This 

 may indeed be true, but it is yet to be proved. 



To apply the discussion to the forms considered in this paper we 

 may ask: Have the spines in Fulgur carica any connection with 

 either copulation or oviposition? Though this question could prob- 

 ably be solved at one of our marine laboratories, its solution has 

 apparently never been attempted. In the absence, then, of definite 

 information on the subject, it is believed that it is pertinent to outline 

 here certain objections which might be raised against the above 

 theory. 



(1) If the spines are caused by oviposition there is a difficulty in 

 explaining their equal development in both the male and the female. 



(2) If the spines are caused by the act of copulation there is likewise 

 a difficulty in explaining their exact similarity in the two sexes. 



To extend our inquiry to Fulgur canaliculatum, it is first to be noted 

 that this species has no true spines. In this form the spines have 

 disappeared, their former presence being shown by the small tubercles 

 which have been crowded back by acceleration into the early whorls. 



