76 Prof. H. James- Clark on the American Spongilla" 



produced by the varying length and breadth of the cell, and the 

 shifting of the relative position of the coarse graniJes. In the 

 inner division (c) of the investing membrane the cells are usu- 

 ally smaller than those in the outer division, but differ in no 

 respect otherwise, either in form or arrangement. They lie 

 flat on their sides in the cytoblastematous layer ; but, except 

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

 underlying brown mass of monad groups and granular inter- 

 stitial substance. 



We have been unable to discover any distinct cell-elements 

 in the cytoblastematous mass immediately around and beneath 

 the monad groups, nor have we found it possible to distin- 

 guish it from the cytoblastema lying on the surface ; and 

 since the continuity between the two is unbroken, we must, 

 perforce, consider 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. 



The Monad Cephalids. — We now proceed to describe the most 

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

 characterizing, 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 correspond functionally to the tentaculated heads 

 of Polypi, and not to their interior epithelial cells. We must 

 first describe what we call the monad-chamber. 



The monad-chamhers (fig. 1, A, fig. 2, fig. 4) are deep 

 spherical 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 circular, areas scattered in pretty close proximity 

 to each other over the " cytoblastemic mass." Each chamber 

 has a single, small, circular aperture {i) which perforates the 

 inner (c) investing membrane, and allows egress into the cir- 

 culatory apartment (/). The aperture {i) 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 per- 



* The hollow groups of monads were originally described by Carter 

 (Ann. & Mag. Nat. Hist., July 1857) as lining a hypothetic vesicle, 

 which he named the "ampullaceous sac." He has since (Ann. «& Mag. 

 Nat. Hist., January 1859) revoked that view and adopted another. We 

 believe him to be, excepting the infen-ed " ampullaceous sac," in the 

 main, right in his first interpretation ; but as our species are different we 

 cannot speak definitely. 



