REPRODUCTION 97 



poda which are naked when full grown, the shell 

 falls off soon after the reduction of the velum. 



With the arrival of adult characters come the 

 characteristic markings and sculpturing of the shell, 

 with its concomitant adornment of spines and pro- 

 cesses when such are produced in the course of 

 growth. In some forms, like the Unionidae, the 

 young shell is at first wrinkled, becoming smooth in 

 later life, and a similar loss of sculpturing is observ- 

 able in some Gastropods (e.g., certain species of 

 Rosiellaria and Ftisus) as well as some Ammonites. 



Arrived at maturity, the final features of the fully 

 formed shell are assumed. The young Cowry shell 

 {Cyprcea) has a thin, sharp lip (Plate XXVI., Fig. 30), 

 which becomes curled inwards and enormously 

 thickened and toothed in the adult (Plate V., 

 Fig. 5). The Scorpion Shell (Pterocera, Plate V., 

 Fig. 11), Strombus (Plate VIII., Fig. 3), Rostellaria 

 (Plate X., Fig. 20), Aporrhais (Plate II., Fig. 3), and 

 others, develop the curious spines and projections 

 that surround the mouth. Rhizochilus, as already 

 noted, attaches itself to the Antipathes, and almost 

 entirely closes the mouth of its shell (Plate XL, 

 Fig. 1). The Land Snails form a thicker lip or 

 narrow their aperture with projecting processes, so 

 that it is a marvel how they pass in or out, and 

 how they can exclude their eggs (Plate VIII., Figs. 

 14-16). 

 7 



