234 THE president's address. 



occur. The subsidiary whorl is occasionally developed between 

 the median whorl and the manubrium, instead of between the 

 median and apical whorls, but I have only seen this in the young 

 spicule (fig. 17) ; or the subsidiary whorl may be missing alto- 

 gether (fig. 21). A curious abnormality is represented in fig. 22, 

 where a branch is given off from near the base of the apical 

 prolongation and the chief subsidiary whorl is defective on the 

 same side of the spicule. 



It is obvious that the form of these spicules is remarkably 

 well adapted to the purpose for which they are employed by 

 the sponge, that purpose being the protection of the external 

 surface. Here they are arranged in a dense forest, with their 

 bases or manubria firmly implanted in the fibrous outer layer 

 of the cortex, and their apices projecting freely. Placed close 

 together, shoulder to shoulder, they form an admirable defence 

 against the attacks of parasites or other enemies. 



In view of their final disposition at the surface of the sp.onge, 

 and the remarkable manner in which their shape conforms to 

 the requirements of that situation, with base and apex each 

 apparently differentiated for its special function, it is not a little 

 surprising to find that these curious organs of defence originate 

 and go through the whole of their development in the interior 

 of the body, beneath the cortex and far removed from the 

 position which they are destined and adapted to occupy. Any- 

 body who cared to speculate about the purpose and intelligence 

 exhibited by sponges would find here abundant material for 

 cogitation. We can imagine him saying " See how the sponge 

 first of all shapes these spicules into appropriate weapons, and 

 then carefully arranges them in their thousands, all in the posi- 

 tion of maximum efficiency ; surely this implies something more 

 than mere mechanical necessity, some purposive action such as 

 we ourselves are capable of performing." It is perhaps quite 

 as remarkable a case as any of those which have recently been 

 brought forward by Mr. Heron-Allen from amongst the Fora- 

 minifera. It is, moreover, by no means unique amongst 

 sponges, for we see the same phenomenon in the case of the 

 cortical layer of sterrasters in the genus Geodia, and other in- 

 stances are also familiar to the student of this group. The most 



