1887.] NATURAL SCIENCES OF PHILADELPHIA, 253 



Trumpet-shaped spicules with very slender, smooth, cylindrical, 

 shafts, (in prepared specimens very generally broken) ; proximal 

 rotules, large, flat or contorted; margins entire or more or less rayed ; 

 distal rotules hardly larger than the diameter of the shaft, too minute 

 to detect any subdivisions. 



After examining some slides of this variety I incidently turned to 

 others of a form collected as an incrustation from some large water 

 pipes, that had conveyed water from the Schuylkill River. The 

 contrast was startling. The skeleton spicules here were short, 

 robust and generally rounded ; the birotulates also were very short, say 

 one half the length of those last described ; shafts thick and widening 

 into each rotule. Rotulse nearly equal in size, margins entire and 

 both of them upturned, saucer-like ; very closely resembling those 

 of M. leidyi. 



This was the major term of the series, and was reached after 

 passing those from the 1800, the 1200, 1000 and 600 ft. altitudes; 

 pausing first at 40 or 50 ft. above tide water, near Bristol, Pennsyl- 

 vania, where, upon a mass of furnace slag, Avas found T. fcmshawei, 

 whose rotules bore the relation to each other of 5 to 6 or 6 to 7; 

 then, in Indian Run, and still later, in tide water in the Schuylkill 

 River below the dam, still greater robustness was reached and the 

 rotulee, found as above, were as nearly equal as those of 3f. leidyi. 



The series was now complete from the last described form, back 

 to that in which the outer rotule, and even the shaft itself, had been 

 nearly eliminated ; while the general features of the sponge, except- 

 ing as to robustness, remained the same. The changes, it will be 

 observed, followed closely the lines of increasing altitude; their 

 cause must be left for later determination. 



The fact mentioned in the early part of my technical description, 

 that specimens of this species are often seen, having their dermal 

 surfaces covered with parallel-lying skeleton spicules, is well worthy 

 of notice. A portion at least, of the skeleton spicules in all sponges 

 seem to have their origin in this dermal film. If, under a high 

 magnifying power, we watch the surface of a sponge that has ger- 

 minated and is growing in a stage tank or other convenient receptacle, 

 we will see these spicules carried about in the amoeboid wanderings 

 of the dermal cells, the end of each multiplying the motion and 

 swaying like the gnomon of a time piece. Under these conditions 

 they are probably prepared, and as the result of these motions they 

 are placed to form the connecting links between the main lines of 



