336 THE INFLUENCE OF LIVING SURROUNDINGS. 



base and at the sides a very variable number of perfora- 

 tions which, in all the works that treat of them systematically, 

 are described and particularly pointed out as specific or even as 

 generic characters. But these holes do not in any way agree 

 with the peculiar characteristics of the families to which these 

 genera belong ; for in Heterocyathus the side walls of the coral 

 ought properly to be quite without perforations, and in Hetero- 

 psammia, which belongs to the group of corals with porous walls, 

 the holes which we find are quite different from those proper to 

 the coral itself. In both cases these perforations, which are 

 clearly visible in the illustration (see fig. 86), are occasioned by 

 the worm, as is plainly shown by their irregularity of number 

 and arrangement. They open directly into the spiral cavity 



FIG. 87. a, a 1 , fleterocya/hus philippensi'i, a fully-grown specimen. At a the hole 

 formed by a Sipunculus is visible in the otherwise solid wall of the cup. b, a young 

 individual showing the terminal hole of the tube of a Sipunculus ; here it is visible in 

 the side wall, but the growth of the coral pushes it to the bottom, c, Heterocyathus 

 pitrtisilictis, established on a species of Cerithium. 



in which the worm lives, and correspond exactly to its growth : 

 that hole which is nearest to the opening of the tubular dwell- 

 ing, out of which the worm protrudes its head, being situated 

 exactly as it must necessarily be with reference to the position 

 of the anus of the worm to serve as a passage for the ejection 

 of excrement. Finally, these holes have 110 connection with 

 the cavity of the coral itself. 



Thus the enlarged foot and the large holes observable at the 

 base or in the sides of the corals, have originated in the same 

 way as those pathological deformities in animals and plants 

 previously mentioned, and this is more particularly proved by 

 the fact that no such holes are formed in the Heterocyathus, 

 which establishes itself on the shells of univalves. But as 



