246 DR. T. ALCOCK ON POLYMORPHINA TUBULOSA. 



ing, tlie shell is fully formed and perfect before this last 

 addition is made to it. There is evidence, however, in the 

 specimens I have now, to show that the animal must have 

 lived for a considerable time in a full-grown state before it 

 thus terminated its existence by producing a permanent 

 likeness of its living self. These specimens have their 

 arched coverings, with the branches proceeding from them, 

 more or less broken away, so as to expose the floor beneath 

 them, which consists of parts of the strong outer wall of 

 the rounded nucleus, and which in all the cases examined 

 presents the same peculiar appearance. It is riddled 

 through with many large holes, sometimes nearly circular, 

 but oftener oval or kidney-shaped, and so numerous as to 

 open a very free communication between the external sar- 

 code and that in the interior of the shell. It is not un- 

 usual to find Polymorphince (of a difi'erent type from these) 

 with a few small round holes in their outer walls ; but 

 they are scattered irregularly, are few in number, and have 

 no evident relation either to one another, or to any 

 structural peculiarity of the animal ; whereas in the present 

 case they are invariably contained within the area of the 

 floor of the covered passages, and are so numerous, and 

 encroach so much on each other, that in some parts they 

 leave only narrow isthmuses of the original shell- wall be- 

 tween them, and the larger holes have every appearance of 

 having been formed by the union of several smaller ones. 

 It is evident from a consideration of their character, that 

 they have been produced by the removal of shell-material 

 previously deposited ; and this gives them a physiological 

 interest ; for though it is natural to suppose that a creature 

 which has the power of precipitating carbonate of lime on 

 its surface would also have the power of removing portions of 

 it by solution or absorption, if required, the foraminifera 

 are so structureless that we should hesitate to attribute to 

 them this function without clear and positive proof. 



