40 U WIIN'i: FAUNA OF ST. ANDREWS. 



Subkingdom MOLLUSC A. 

 Section I. MOLLUSCOIDA. 



Class I. POLYZOA. 



The majority of the Polyzoa come from the deep water ot 

 the hay; and, indeed, there are comparatively few to be met 

 with between tide-marks that do not also occur in the former. 

 The minute animals of the calcareous masses so characteristic 

 of many of this group, perform none of those alterations on 

 the surface of the earth which the equally tiny coral-polyps 

 daily effect; yet their workmanship in our northern waters is 

 as regular and beautiful as that fashioned by the latter in the 

 tropical seas. The patterns of the Lepralia-, for instance, 

 excite admiration ; and though the apparent resemblance in 

 growth, superficial aspect, and position may suggest to some 

 an analogy between them and the lichens of our rocks 

 and trees, yet it is remote and unable to bear close criti- 

 cism. It is true it is difficult to assign an exact function to 

 these organisms ; but in some cases the calcareous crust of 

 the Lepralia', affords a better hold to many stationary marine 

 animals than the rock itself. Moreover, after heavy-coated 

 forms (like the Balani) have reared themselves on this basis, 

 it frequently happens that the original crust is loosened from 

 its attachment, and both fall off together. The coating of 

 Lepralice, also, may prevent to some extent the disintegration 

 i it' soft rocks and stones. By removing a portion of bark with 

 in adherent Balanus from a submerged thorn-tree, and care- 

 fully detaching the former, a fine network of Lepralia is found 

 lowest, then the calcareous coating of the Balanus; and if 

 tlir latter has perished, a rough layer of Cellepora jmmicosa 

 obliterates all trace of it from without. 



The Chcilostomatous Polyzoa are fairly represented ; and 

 several, e. g. F/ustra and Gemellaria, occur in vast quantities 

 attached to stones, shells, and corallines on the West Sands 

 after storms. The majority are common to the eastern shores, 



