The American Sjjonffilla. Ill 



on the extreme border, and then an actual break in the continuity 

 of the investing membrane becomes evident. 



Entering this aperture we do not meet with any obstacle for a 

 little distance around it ; there is a clear open space (Fig. 4) ; but 

 pressing onward beyond that, either to the right or the left or 

 directly forward, the cavity apj^ears filled by a collection of vibrat- 

 ing bodies. They seem to be arranged radiatingiy from and about 

 the centre. Close inspection, however, modifies this view, and it 

 turns out that they are based upon the periphery of the chamber, 

 and converge towards its centre, where is a small unoccupied space. 

 We presently recognize these converging bodies to be craspedote, 

 fiagellate monads {j), so closely packed together, side by side, as to 

 form a continuous stratum (Figs. 2 and 4) over the whole concave 

 face of the chamber, excepting immediately about the aperture. 

 Every feature of the monad is strongly marked ; even the cylindri- 

 cal collar is so heavy and conspicuous that its outlines may be seen 

 •with as low a power as two hundred diameters. We have studied 

 these bodies with a |th-inch objective, and found it not at aU dif- 

 ficult to focus down upon the details of their organization, without 

 pressing upon or even touching the specimen. 



These monads are in every general essential identical with those 

 which we originally found in Leucoselenia, and like those also, 

 recently described by Carter,* in Grantia compressa. They are 

 attached to the concave face of the chamber by their posterior end 

 (Fig. 4,y) ; and the anterior extremity, with its flagellum (Fig. 3, 1) 

 and collar (h), projects freely into the open space, and toward the 

 centre of the apartment. When fully expanded, the length of the 

 body and collar together is about one-third, or a little more, of the 

 diameter of the chamber ; so that nearly one-third of the latter is 

 unoccupied at the centre, except by the tips of the flagella converg- 

 ing from every direction. As the monads lie touching each other 

 on every side (Fig. 2), they mutually flatten their bodies, some- 

 times so much as to give them a strong polygonal outline ; or, when 

 the whole mass is expanded, they scarcely impress each other, and 

 therefore retain a rounded contour. By plunging the focus so as to 

 look into the aperture of a chamber, down upon the monads at the 

 bottom (Fig. 2) of it, an end view of each cephalid is obtained. 

 From this point the foreshortened cylindrical collar looks like a 

 strong, dark circle (Fig. 3 a, h), which retains its conspicuousness as 

 we plunge down farther, even to the base, where it is attached to 

 the body {j). The outline of the latter is considerably without the 

 " dark circle," the two being concentric to each other. At the same 

 time we see in the centre of the dark circle a black spot (Z) which 

 may also be focussed up and down upon, and hence it is inferred 

 to be a continuous line foreshortened. Other views (Fig. 3, 1) con- 



* 'Ann. Mag. Nat. Hist.,' July, 1871. 



