390 BULLETIN OF THE UNITED STATES PISH COMMISSION. 



ally seen upon the bottom of pools and streams, ot dense masses of 

 water-moss, may momentarily mislead the collector; but a pocket lens 

 v. ill reveal to him at a glance the minute leaves of the moss, or the deli- 

 cate green threads of the algae; while in the true sponge he will hardly 

 fail to see the characteristic pores penetrating its surface and to detect 

 the fine points of numerous projecting spicules. 



The particular feature distinguishing fresh-water from marine sponges 

 is the presence in the former, when mature, of the reproductive bodies 

 known as statoblasts or statospheres. These are nearly spherical, light 

 or dark brown, generally easily visible by the naked eye. and occupy 

 positions at the lower surface or throughout the mass of the sponge. 

 1 hey should be carefully looked for and gathered with the specimen, 

 ;is it is upon the form of the spicules encrusting their surface, that the 

 classification of fresh-water sponges principally depends. Either very 

 early or very late in the season minute groups of these statospheres 

 may often be found, unaccompanied by the skeleton spicules and slime- 

 like flesh of the sponge, and it is well worth while to gather and pre- 

 serve them. 



These sponges are found growing upon any supporting substance ex- 

 cept mud, and at every depth beneath the surface of the water; but they 

 affect chiefly the under and upper surface of stones and timbers, the 

 sides of piling, and of submerged stumps and branches. The stems and 

 roots of water plants are often coated and matted together by them. 

 As the silting of earthy matter into their pores would soon suffocate 

 them, we find in standing pools the most flourishing specimens attached 

 to the under side of stones or water-logged timbers, which shield them 

 from the intrusion of the heavier silicious particles; whilst in clear lakes 

 and rapidly flowing streams they plant themselves boldly upon the 

 upper surface of stones in the full sunlight. 



A further hint as to the bodies of water which favor their growth 

 may be found in the fact that three species, one of them the most pecu- 

 liar of American forms, were found in a stream a child could step over; 

 five were gathered at one time in the submerged cellar of a burnt mill; 

 while the timber work of the dams upon some of our largest rivers has 

 furnished rich collections; so that there is scarcely a situation where 

 water stands or runs, excepting upon the muddy bottoms of shallow 

 streams or mill-ponds, where sponges may not be hopefully sought for 

 and frequently discovered. 



The best season for collecting sponges varies with the different species, 

 but may be generally stated to be from the last of July to the middle 

 or latter part of November, when the spicules and statospheres are 

 likely to be fully matured. They may be preserved in dilute alcohol 

 or dried by a few days' exposure to the air; in which condition (as the 

 personal "application" of the foregoing sermon), the writer would be 

 \ ery happy to receive specimens from all parts of this and other coun- 

 tries. If packed in light boxes, strong enough to prevent crushing, the 



