110 The American SpongiUa. 



but, altliougli suspecting it of such a function, we could detect no 

 change other than might be produced by the varying length and 

 breadth of the cell, and the shifting of the relative position of the 

 coarse granules. In the inner division (c) of the investing mem- 

 brane the cells are usually smaller than those in the outer di^-ision, 

 but differ in no respect otherwise, neither in form nor arrangement. 

 They lie flat on theu' sides in the cytoblastemous layer ; but, except 

 in profile, they are most difficult to discover on account of the 

 underlying brown mass of monad groups and gi'anular interstitial 

 substance. 



Although we have been unable to discover any distinct cell 

 elements in the cytoblastematous mass immediately around and 

 beneath the monad groups, neither have we found it possible to dis- 

 tinguish it from the cytoblastema lying on the surface : and since 

 the continuity between the two is unbroken, we must, perforce, con- 

 sider them as one. The underlying portion of the cytoblastematous 

 mass, however, is characterized by irregularly-scattered, moderately 

 coarse, brown granules (c'). These serve very well as a dark frame 

 or setting to the monad chambers (A), and by contrast bring them 

 out more strongly. 



17^6 Monad-cejjhalids. — We now proceed to describe the most 

 essential feature of this animal, the monads. They are the cha- 

 racterizing, the dominating element, in reference to which the whole 

 organism is contrived and constructed. They are not cells; they 

 are the heads of a polycephalic individual, and consequently cor- 

 respond functionally to the tentaculated heads of Polypi, and not to 

 their interior epitheUal cells. We must first describe what we call 

 the monad chamber. 



The monad chamhers (Fig. 1, h ; Fig. 2 ; Fig. 4) are deep sphe- 

 rical hollows which form the receptacles of the groups of monads {j). 

 They are mere cavities, and have no lining wall.* They may be 

 easily recognized, in young specimens, as clear, more or less chcular, 

 areas scattered in pretty close proximity to each other over the 

 " cytoblastemic mass." Each chamber has a single, small, chcular 

 aperture {i) which perforates the inner (c) investing membrane, 

 and allows egress into the cii-culatory apartment (/). The aperture 

 (*') varies in size at times, and may even be completely closed. We 

 have never seen it open wider than one-third the diameter of the 

 chamber, and very rarely more than one-fifth as wide. That it is 

 a true perforation, and not a clear sjiut, may be demonstrated by 

 bringing a chamber into profile, so that its apertm'e (Fig. 4, i) lies 



* The hollow groups r f monads were originally descrihed by Carter (' Ann. 

 Mag. Nat. Hist.,' July, 1^57) as lining an hyijothecatcd vci-iele, which he named 

 the " ampull;:ceoiis sac." He has t-ince (• Ann. Mag.,' Jan., lh'59) revoked that 

 view and adopted another. We believe him to be, excepting tiic inferred ''ampul- 

 laceons sac," in the main, ri;iht in h's first interpretation ; but as our species are 

 diffeient we cannot speak dtfinitt ly. 



