304 FRESH-WATER BIOLOGY 



Those who wish to gather specimens for their cabinets or design 

 to determine genera and species must await the maturity of the 

 various specimens. Observation seems to make it probable that 

 the rarer, filmy sponges complete their growth and mature their 

 gemmxiles earHer than the more lusty, massive forms. The gem- 

 mules of the former have often been seen in August or September 

 resting in slender Hnes upon standing or floating timbers from 

 which the rest of the sponge has disappeared, though the coarser 

 forms are frequently immature late in November. These dates 

 hold true for the northern United States generally and would of 

 course vary in other parts of the world; but there are undoubtedly 

 individual regions of extreme or atypical climatic conditions within 

 our own area where the sponge calendar when worked out will show 

 a distinctly individual aspect. 



A hint as to hopeful locaKties for collecting may suffice. Do not 

 waste time in hunting along sluggish streams or in shallow, muddy 

 ponds, where, even if the sponges start to grow, they wiU soon be 

 suffocated by gravitating particles of earthy matter. A reserva- 

 tion should perhaps be made in favor of the lower sides of floating 

 timbers that have long lain in the water, since here gravity protects 

 instead of injures the sponges. Only one other caution seems neces- 

 sary. As all known fresh-water sponges are siHceous the student 

 wfll probably fail to find them in waters strongly impregnated with 

 carbonate of lime, though they are recorded from such places. 



Perfect drying is to be recommended. The proper classification 

 can be as readily determined from dry as from fresh sponges and 

 it is only when a specimen has some novel character or specific 

 form that it is worth while to preserve it in alcohol. When a 

 wrapper is necessary for transportation or otherwise, be siixe to 

 use soft paper, rather than cotton or sawdust. 



Other features having proved indeterminate or imreliable, the 

 system is based upon the shapes and positions of the minute spicules 

 foimd embedded in the gemmule crust. As these can only be sat- 

 isfactorily seen when the impenetrable crust is made transparent 

 or removed, three microslides from each specimen must be pre- 

 pared to determine the forms of the skeleton, the dermal or flesh, 

 and the gemmifle spicules. 



