40 THE president's ADDRESS. 



tion in the degree of degeneration of individual rays. I have 

 recently, however, come across a case — not, indeed, unique — 

 in which I think the variation in the number of rays must 

 have originated discontinuously, or in other words, by mutation 

 One of the most characteristic spicules in the genus Tetilla is 

 the anatriaene or grapnel spicule, a modified tetract which 

 usually has a very long, slender shaft and three short, 

 recurved, hook-like cladi. In Tetilla pilula, although the 

 entire sponge is very small, there are probably some thousands 

 of these grapnel spicules in a single specimen, but they are 

 not typical grapnels, for in every case observed only a single 

 cladus is developed, the other two have disappeared, without 

 leaving the slightest vestige to indicate their former presence. 

 Only three specimens of this sponge are known, but all agree 

 in this peculiarity, the anatriaene has become an anamonaene. 

 Another form of triaene, the protriaene or pitchfork, occurs in 

 the same species, and these retain the full number of cladi. 



In the closely related genus Cinachyra similar triaenes occur, 

 and in a species which I have recently been investigating and 

 shall shortly describe under the name Cinachyra vaccinata, three 

 kinds are found, ana triaenes and large and small protriaenes, and 

 all exhibit a striking peculiarity in that the apex of the shaft, 

 which in other species tapers to a fine point, is conspicuously 

 enlarged like a handle. I have two specimens, each containing 

 an enormous number of these spicules, and I have seen no excep- 

 tion to this rule. 



One more illustration must suffice. Species of the genus 

 Esperella (Mycale) possess a somewhat varied assortment of 

 spicules. The typical megasclere is a style, with rounded or 

 enlarged base and evenly pointed apex. Amongst the micro- 

 scleres occurs the widely distributed sigma, a C-shaped or S-shaped 

 hook, pointed at each end. In the closely related genus 

 Paresperella the back of the hook, just where it curves round 

 at each end, is provided with teeth like a saw, and, curiously 

 enough, in one of the two species which I have examined, the 

 apex of the style is usually provided with two teeth, and in the 

 other with one. There seems to be a correlation here between 

 the modification of the si^ma and that of the style, just as in 



