294 PROCEEDINGS OF THE 



tary read the annual report. This was considered very satisfactory. 

 There was a small increase in the membership, the resignations 

 had been but few, though the loss by death had been somewhat 

 more than usual, while the number elected was greater than in 

 the previous year. The attendance at the meetings was good, and 

 there was a satisfactory list of communications and exhibits. 

 The excursions had been well attended. The librarian reported 

 that the number ef books borrowed from the library showed no 

 diminution. The curator reported that a large number of valuable 

 micro-slides had been added to the Cabinet, which now contained 

 over 8,000 specimens. The treasurer's accounts and balance-sheet 

 showed that though the finances were somewhat affected by the 

 prevailing difficulties, they were in a perfectly sound condition. 

 The adoption of the reports and balance-sheet was duly moved 

 and carried. 



Prof. Dendy then gave his presidential address. The title was 

 " The Chessman Spicule of the genus Latrunculia ; a study in the 

 origin of Specific Characters." He said : "It is very well known 

 that there are certain types of tetraxonid microscleres in which 

 the spicule consists of an elongated, rod-like axis with whorls of 

 outgrowths upon it. As a result of a study of some novel varieties 

 of this type it occurred to me that the position of these whorls 

 might correspond with that of the nodes in a vibrating rod, and 

 that thus the form of the spicule might be largely determined by 

 a well-known physical cause, the deposition of silica taking place 

 chiefly where the rod was in a state of rest. The stream of water 

 flowing through the canal system of the sponge seems to afford a 

 sufficient explanation of such vibration, for the spicules are em- 

 bedded in the very soft, gelatinous mesogloea in the immediate 

 neighbourhood of the canals. I was led to make a somewhat 

 elaborate study of the so-called ' chessman ' spicule in two species 

 of the genus Latrunculia, and the development of these proved 

 to be extraordinarily interesting. A good deal has been written 

 on the development of sponge spicules, and some of the published 

 accounts appear to be very contradictory. It would seem that 

 this development is by no means so simple an affair as is often 

 supposed, but is in reality a very complex process, the course of 

 which is determined partly by physical and partly by what may 

 be called biological factors." 



The two species, Latrunculia bocagci and L. apicalis, were ob- 



