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 Unionide, the 
young shell is at first wrinkled, becoming smooth in 
later life, and a similar loss of sculpturing is observ- 
able in some Gastropods (¢.g., certain species of 
Rostellavia and Fusus) as well as some Ammonites. 
Arrived at maturity, the final features of the fully 
formed shell are assumed. The young Cowry shell 
(Cyprea) 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), Stvombus (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 XI., 
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 
