106 The American Spongilla. 



polycepbalic unit. Yet, whichever view prevails, the tendency is 

 the same, and the Polyp theory is negatived most unquestionably. 

 The incompatibility of the interior organisms of the two groups, 

 above mentioned, is so great that it would seem as idle to elaborate 

 a proof of it, as to attempt the demonstration of an axiom. The 

 question is really circumscribed, according to the method of Haeckel, 

 to arguing that, since a system of branching canals in the Sponge 

 reminds one very strongly of the intricate network of passage-ways 

 in the basal parts of certain Polyps, therefore the two are homo- 

 logous, and bear an identical relation to the rest of the organism 

 Carter* has answered this far-fetched homology with considerable 

 detail in a recent paper ; and we do not therefore feel called upon 

 to add more to it. 



The principal aim of this article is to furnish new material in 

 proof of the polycephalism of the iSpongiae, and particularly in 

 regard to their relation with the Protozoa Flageilata. We are 

 highly pleased to find that Carter has latelyf confirmed our earliest 

 observations^ as to the organization of the collar-bearing monads 

 of Leueoselenia, by an investigation of Grantia com'pressa. He 

 has also accepted our interpretation of the horn-like processes of 

 the sponge-cell of Spongilla alba ; that they are the outlines of a 

 membranous collar in profile. 



We have now to bring forward a fourth example of a cras- 

 pedote, flagellate monad-cephalid in a Sponge. It seems to be a 

 Spongilla, but specifically, at least in its monads, it differs from the 

 English forms. For convenience sake, we will call it Spongilla 

 arachnoidea, from its resemblance to an irregular spider-web. It 

 lives in fresh-water streams and ponds, usually about the bottom of 

 the stems of water-plants, or wherever there is considerable shade ; 

 apparently avoiding the light, as we seldom, if ever, found it in 

 open water. In size it varies from a few inches to half a line in 

 diameter; of no definite shape; and has a uniform fuscous or 

 yellowish-brown colour ; and is wrapped about by a filmy, trans- 

 parent, colourless envelope (" investing membrane " Carter). The 

 brown colour is inherent to the interior mass, in which the groups of 

 monads are imbedded ; in fact, the latter are themselves as strongly 

 coloured by brown granular contents. The " investing membrane " 

 is also slightly tinged with amber colour by the large and small 

 spicules which are imbedded in it. Excepting in very small 

 specimens, foreign matter is often so thickly spread over the surface 

 as to obscure the view and seriously interfere with a correct inter- 

 pretation of the relation of parts. We have been most fortunate 



* "On New Sponges, &c.," 'Ann. Mag. Nat. Hist.,' July, 1871. 

 t m sup., July, 1871. 



j 'Memoirs Boston Sec. Nat. Hist.,' vol. i., 1867, "On f .e Sponjiae Ciliatse as 

 Infusoria Flageilata." 



