86 A. H. MACK AY ON 



dams aud in streams which can be stepped across. They are found in the stagnant pool 

 and breasting a strong current. They encrust with green the surfaces of pebbles in the 

 margins of our lakelets, or speck with patches of dull cream or gray or white their under- 

 sides. The author dredged some from a depth of forty feet in Grand Lake, Nova Scotia, 

 and from nearly as great a depth in Newfoundland. More time and patience might 

 doubtless have been rewarded by specimens from a greater depth, had a pebbly or rocky 

 bottom or a water-logged timber been scraped in our course. The deeper bottoms (in a few 

 cases over two hundred feet) were generally characterized by extensiA'^e deposits of 

 diatomaceous slime or mud. Dybowski, when dredging in Lake Baikal, Central Asia, 

 brought np some s]5ecimens, stunted and nearly colorless, from as great a depth as 300 

 feet ; but only from an area of the liottom not mud-i'overed. 



Collecting. — Sponges should be collected attached to their base of support when- 

 ever possible. They may be preserved by immediate transference to alcohol ; or in just 

 as serviceable a manner for most purposes, and more conveniently, by immediate aud 

 thorough drying in the sun or by artificial heat. "When thoroughly dry, they can be 

 preserved for an indefinite period. Care should be taken to protect them from diist, aud 

 if the natural green color is to ])e retained, from the light also. 



Genekal Characters. — Without attempting any outline of the histology, physi- 

 ology or development of the Spougillidae, it may be desirable to call attention to a few 

 conspicuous characters. In connection with all the Porifera, their spicule-supported 

 liesh is traversed by a system of incurrent and excurrent canals, through which there is a 

 circulation of water from which is derived the material for the growth of their definitely 

 organized sarcode, their spicules and their reproductive elements. In winter, as a general 

 rule, this sarcode disappears. The skeletal and dermal or flesh spicules are thus set free, 

 and are eventually deposited by the water where sediment is accumulating. They are 

 often carried by the water currents into the substance of different species, and may thus 

 ffive rise to errors if their extraneous origin is not detected. In the diatomaceous muds 

 aud earths found in more or less abundance in all our lakes, these spicules are generally 

 found. Sometimes they form quite an appreciable percentage of the siliceous organic 

 remains in these so-called infusorial deposits. The spicules are of colloidal silica — 

 miueralogically considered, opal, — the silica of which ultimately came from its solution 

 in the water, from which it was secreted and built up by special cells into transparent, 

 flinty, symmetrical forms. The skeletal spicules of the more abundant species in Canada 

 are Oxeas (the sharp-pointed form of Prof Sollas's Monaxon diactine) — needles sharp at 

 both ends — the one-hundredth of an inch in length, or slightly more or less, smooth or 

 variously microspined, straight or slightly curved, slender or robust, separate or overlap- 

 ping each other in linear fascicles, aud slightly cemented together. 



Dermal or flesh spicules are found in some species, while they are absent in others. 

 They are very much smaller than those of the skeleton — in one species as short as 00006 

 inch. They are found free at the dermal surface or within the flesh. In our species they 

 are either minute acerates or birotulates. 



During the summer and autumn, clusters of elementary cells appear at points within 

 the sarcode. They soon become invested with more or less spherical chitinous capsules, 



