216 PROCEEDINGS OF THE ACADEMY OF [1887. 



confess my inability, as yet, to answer the question. If freshness of 

 appearance is taken as a guide, the latter seems the more probable 

 supposition. Numbers of gemmules without capsular covering are 

 to be found in both situations and the foramiual openings, which 

 may be said to be generally upon the upper side, are found in 

 some parts of the series upon the lower. The problem remains 

 open. 



The peculiar markings upon the external surface of the sponge, 

 f(H-m anothpr perplexing feature. Upon other sponges we see the 

 terminations of submerged canals, partially exposed by the rupture 

 of the thin dermal film which alone covered them ; here, the mark- 

 ings consist of spicular ridges, sometimes slightly grooved along 

 their summits, and terminated at their divergent extremities by in- 

 clined efferent (or afferent?) orifices. Those who are familiar with 

 the appearance of young, living sponges of other species, wall re- 

 member that the dermal film is supported upon the points of pro- 

 jecting spicules, at some distance above the denser mass of the sponge, 

 which it thus "tympanizes," to use a happy expression of Mr. Carter. 

 The vestibule thus formed in or around them, is, in M. leidyi, prob- 

 ably on account of the shortness and non-fasciculated character of 

 its spicules, almost or entirely wanting, and its place seems to be 

 supplied when alive by the formation along the above-mentioned 

 ridges, of external, sub-cylindrical, convergent canals that have not 

 been mentioned in any other species. Upon the only occasion in 

 which I was able to experiment upon a living sponge in this condi- 

 tion, I was puzzled to see the particles of carmine used in feeding 

 it, drawn through the pores into these channels and presently suck- 

 led downward into the body of the sponge, instead of being borne 

 forward and thrown out from them through a common orifice or 

 -chimney, as is familiar in other cases. Attempting no explanation 

 of this reversal of ordinary methods, I merely record it as an excep- 

 tional fact. 



Within some fragments collected at "Windmill Island, were found 

 many subspherical masses, like large shot, each containing three or 

 four gemmules, embedded, not in j^arenchymal cells, but in a dense 

 mass of skeleton spicules. These have not been seen elsewhere. 



Some question has been raised as to the presence, in parts of this 

 species, of spined skeleton spicules. As the result of a careful ex- 

 amination of large numbers of specimens I may state my belief that 

 any such appearance has been due to the accidental intrusion of 



