The American Sijongilla. 105 



comparable with similar canals in tlie polyjmlom of Halcyonai ians : 

 and, by implication, that tlie cilia-bearing cells of the interior lining- 

 wall of the Zoophyte find their homologiies in the ciliated, cell-like 

 bodies of the interior chambers of the Porifera. If, now, it should 

 turn out that these last are not altogether mere cell-components c f 

 a tissue, but are each, severally, an independent body, although 

 closely connected with others in a common bond, then the attempted 

 parallelism between the two groups must utterly fail of confirma- 

 tion. The tendency of Carter's later investigations, and our own 

 too, is to show that this is no vain supposition. 



For ourselves, we hold that each ciliated hodij of the Sponge 

 is a cephalic member (a cephalid in this case) of a polycephalic 

 individual.* We believe, as f;^r as we can understind his un- 

 decided, rather hesitating position. Carter's latest decision is, that 

 the Sponge is a community of Amoebous individuals,! and not a 



EXPLANATION OF PLATE XI. 



SjMnjilla arachnoidea Jas.-Cl. 



The following letters apply to identical parts in all of the Figures: — 'i, Invest- 

 ing membrane : outer division. — ci^. Sectional profile of the cytiihlastema of ". — ■ 

 6, Cells in the thickness of a. — h\ Cells (like those at b} about the spicules (c). — 

 6^ Cells of the investing membrane, with their nucleus ; a surface view. — b^, Tem- 

 porary junction (by contact only) of the outer («) and inner (c) divisions of the 

 investing membrane. — c, Investing membrane ; epitlielioid inner division, in slc- 

 tional profile. — c^. Interspaces between monad chambers. — (/, Junction of the 

 divisions of the investing membrane along the spicules. — c, Larger spicules. — 

 c', Smaller spicules. — f. Circulatory apartment. — g, Monadigerous niass. — A, IMonad 

 chambers and monad groups — /, Aperture of h. — j, Monads, or the body jirojjer 

 in Figs. 3 and 3 a. — k. Cylindrical c dlar of j. — /, Flaijellum. — n, Nucleus. — 

 OS, Minor ostioles. — v. Contractile vesicU^s. 



Fig. 1. — Magnified 320 diameters. Part of a very young Spo7i:]ina, of an oblate 

 spheroidal form, and about ^rWh of an inch in diameter. On the right is presented 

 a face view of the investing membrane and tlie underlying monadigerous m:iss. 

 On the left the focus is so adapted as to be fixed on a face view of the monad n.ass, 

 and at the same time on a sectional profile of the investing membrane at a', 6*, c, 

 and (7. 



Fig. 2. — Magnified 780 diameters. Interior of a monad chamber, seen thiough 

 the aperture ; the monads appear in end view, and ciowded together side by side 

 like a pavement work. 



Fig. 3. — Magnified IGOO diameters. A single monad, as seen in profile in the 

 monad chamber. Only two cfmtractile vesicles were present in this sj^ecimen. 

 The cylindrical collar (A) is extended to its utmost. 



Fig. 3rt. — Magnified 1600 diameters. Foreshortened, front view of a monad; 

 the body (j) in the distance ; the hollow cylinder (A) projecting toward the observi r 

 like a dark hoop, and iXie flagelluia {i) in the centre appearing as a black spot. 



Fig. 4. — IMagnitied 780 diameters. Sectional view of a monad ch.amber, bringing 

 the aperture (') into profile, as well as the monails which lie at the same level ; 

 thus showing their conveigeuce about the central open space. 



* See article on " Polarity and Polyccplialism," ' Silliman's Amer. Journal,' 

 January, 1870 



t See Carter "On Fecundation in the two Volvoces;" "On Eudorina, Spon- 

 gilla, &c.," 'Annals ami Magazine Nat. Hi.'it.,' January, 1859; also for July. 1871, 



" On New Spongt.s, &c." 



I 2 



