REPORT OF THE DIRECTOR I916 I 79 



These ontogenetic traits are brought out emphatically and beauti- 

 fully in the specimens now under consideration. Here is a very 

 strongly nodose and a very deeply annulate species in which the 

 slightly modified, early and infantile expression of growth is con- 

 tinued for a long period, the lower obcones being smooth or faintly 

 prismatic. In one of these this infantile condition is maintained for 

 fully half the length of the completed skeleton, while in the other 

 it covers a less proportion — one-third of the full length of the 

 sponge. Thereupon follows, at the upper end of the obcone, the 

 primary development into nodes, and directly thereafter, the con- 

 strictions which are to produce the annulations. Over these annula- 

 tions, constrictions and nodes run the prism lines in the usual 

 manner characteristic of all the nodose species of this genus 

 Hydnoceras. 



The smaller of the two specimens under consideration (that at 

 the left of the drawing) is actually complete so far as its length is 

 concerned and the distal or upper extremity is the entire margin 

 of the osculum of the sponge itself. The specimen presents other 

 features of maturity and decline which are highly instructive. The 

 first three of the annulations, counting from the bottom, are broad, 

 their nodes are blunt ; but therewith onward the constrictions 

 become deeper, the annulations narrower and sharper, the nodes 

 relatively smaller. The gradual decline in the prominence of the 

 nodes is obvious, and in the seventh and eighth rings the nodes 

 show distinct signs of suppression ; in the eighth or terminal ring 

 a suppression which indicates a tendency to complete extinction 

 in further growth, had such further growth continued. This con- 

 dition is likewise true of the rings themselves, and accompanying 

 all this general decline after the adult development of the skeleton 

 midway of its length, is its loss of diameter, approximating again 

 in this respect the infantile condition. The specimen thus quite 

 emphatically and unusually shows the unfolding of the general 

 morphological characters of the genus and species in regular order 

 through the nepionic stages into the mature, and then their equally 

 gradual decline from the mature ontogeny into the gerontic or 

 senile stage. 



This evidence thus ties together a good many outstanding scat- 

 tering data, regarding the structure of these sponges and the true 

 relations of their individual development. The special interest of 

 this specimen is that it helps to interpret the morphologic value of 

 the sponges of this class; that is to say, here is a sponge, obviously 



