318 PROCEEDINGS OF THE ACADEMY OP [1884. 



ness, and a foot or two in diameter, represent the aggregation of 

 several ^^ears. In a few places, at tlie base of the walls, the pale 

 green branches of Spongilla lacuatris could be seen, and occa- 

 sionall}', to the speaker's surprise, slender waving processes of the 

 same species, totally colorless, could be seen reaching up through 

 the mud in little groups upon the bottom. He was surprised, 

 because he had always held that it was impotsible for sponges to 

 live upon a muddy bottom, and theoretic reasoning would still 

 suggest that probably only this species, which can thus hold itself 

 up out of the suffocating silt, can survive the constant deposition 

 of siliceous particles. The total amount of sponge growth was 

 relatively small, and the probability of an aqueous taint from it, 

 very remote. 



The commensal habit of many of the lower animals who feed by 

 the creation of ciliary whirlpool currents, has been frequently 

 referred to ; the weaker current-makers, such as vorticell0e,stentors, 

 and the errant and tubicolous rotifers, planting themselves about 

 the heads of the stronger pol^'zoa to supply their own nets with 

 what may have escaped from the others. The same instinctive 

 principle which leads all these to locate themselves most plenti- 

 fully amongst the stones in the rapids of streams, was particularly 

 noticeable in promoting their aggregation upon and in the neigh- 

 borhood of the inlet and outlet gates of tiie reservoirs. The feeble 

 currents produced b}' each can only bring within its reach the 

 floating provision from a! very limited area; the volume of water 

 poured through these gates brings to them a rich supply, and the 

 numbers and variety of these organisms increase in proportion. 

 Of the fixed forms were seen amongst the bryozoa, beside one or 

 more undetermined species of Flumatella — Pectinatella magnifica 

 and Urnatella gracilis of Leidy, and the newly described Palu- 

 dicella erecta. Attached to these were Yorticellae, Epistilis and 

 Stentors innumerable; Pyxicola SLud Acineta; rotifers of various 

 names, including prominently Limnias and other, probably unde- 

 scribed forms among the Melicertidse. Very abundant among these 

 was the interesting chsetobranch annelid, Manayunkia speciosa 

 Leidy, which has of late been frequently noticed in this vicinity, 

 and the wonderfully marine-looking hydroid Cordylophora lacus- 

 tris. This last was particularly abundant around the southeast 

 outlet ; its stems forming a complete matting over many yards 

 of surface, commingled with br3'ozoa and sponges in intricate 

 confusion. 



A large valve had been removed from a discharging main on the 

 southern side of the reservoir hill, a hundred yards or more from 

 the opening in the bottom of one of the basins, and where all light 

 was consequently absent. An incrustation, averaging perhaps 

 three-eighths of an inch in thickness, upon the inner surface of this 

 valve, was found to be largely composed of the gemmuhe and 

 spicules of Meyenia Leidyi ; mingled with which were stems of 



