74 Harvey B. Holl — On Foml Sponges. 



openings, but tlie study, of the recent species has enabled Dr. Bower- 

 bank to ascertain that this is not the case, and that in the tubular and 

 cyathiform sponges, those only which open into the cavities appertain 

 to efferent canals ; while those situated on the exterior lead into the 

 canals which are destined to give passage to the incurrent streams of 

 nutritive fluid. In all the tubular and cup-shaped sponges, therefore, 

 their office may be inferred by their position. In the amorphous 

 sponges they are scattered over the surface either singly or in groups, 

 sometimes on mamillary elevations or ridges, sometimes in pits or 

 depressions, and are probably ejaculatory orifices, imbibition taking 

 place through the pores and interstices of the sponge skelet(ni. They 

 are permanent organs, and vary greatly in size, proximity, and regu- 

 larity in their distribution. Occasionally several grooves radiate from 

 the margin of the oscule, and in other species there is no distinct 

 orifice, but the grooves terminate internally in three or four small pores, 

 wliich then supply the place of the single oscule; but even these are 

 sometimes scarcely i)erceptible, as in the Silurian Stromatopora (Stelli- 

 spongla) cnnsteUuta (Hall). These stellate grooves, or " Sillom, " are 

 not, however, physiologically distinct from the oscules ; and the 

 smaller grouped tubules, as for instance those in Jerea (Polypothecia) 

 dichotoma (Bennett), and' J", pyriformia (Lamour), etc., do not differ from 

 oscules, except in their greater length. 



4. Tiie Pores. — Besides the oscules, palcontological writers are in the 

 habit of speaking of the pores. It must be understood, however, that 

 by this term they designate not the temporary openings in the sarcode 

 of the animal during imbibition, to which it is properly applied, but 

 merely the interstices in the tissue of the skeleton in the dead sponge ; 

 for in the living state these interstices are more or less completely filled 

 with the sarcode. In some sponges there are no orifices, either of incur- 

 rent or excurrent canals, that are distinguishable either by form, size, or 

 position, from the ordinary interstices of the sponge tissue, the whole 

 being formed of a nearly uniform rete ; and in these cases the pores 

 or interstices must supply the place of the larger orifices, although 

 closed by the sarcode during the intervals of active inhalation and 

 exhalation ; moreover, in those sponges possessing well marked 

 incurrent orifices it is still probable that the whole of the external 

 surface is more or less an inhalent one, through the interspaces of the 

 rete, according to the exigencies of the animal. 



5. The Epitlieca. — Among the fossil sponges some portion of tlie 

 surface, especially externally, toward the base, is frecpiently observed 

 to be either without pores or they are so minute as to be invisible, 

 and the sponge then appears as though covered by a more or less smooth 



