Distribution of Saccammina sphwrica, etc. 17 



externally from Wehhina heviis}:)h /erica only by tlie nature of tlie 

 shell-wall, which is unpolished and porous, and quite unlike the 

 hard and closely cemented tests of Wehhina. We figure a series of 

 specimens selected from various dredgings, representing the tran- 

 sition from the roughlv arenaceous to the perfectly smooth test 

 (Plate II, figs. 10-16). 



The existence of such a series makes easy of comprehension a 

 point which has troubled many students of the Rhizopoda, viz. : 

 how do the pseudopodial extensions of the protojilasm of the 

 animal gain access to the surrounding water, in the absence of any 

 definite general aperture? The necessity for such an aperture 

 appears to have impressed itself strongly, in the first place upon 

 Brady, who, however, came to the correct conclusion that the inter- 

 stitial cement was finely porous, though even he seems to have 

 thought it necessary to postulate " interstitial orifices " — whatever 

 they may have been. It impressed itself still more strongly on 

 Dr. Ehumbler, to whom the absence of a definite orifice in his 

 Primativgehduse appears to have presented a serious difficulty. 

 He assumes, or supposes, that "the pseudopodia are extruded 

 along the edge where the primitive shell-cover touches the base 

 upon which the young animal builds its house." There is, liow- 

 ever, no doubt in our minds that the protoplasm of the Foramini- 

 fera is capable of protrusion through passages of an infinitesimal 

 diameter, such as would occur between the extremely minute 

 grains which constitute a cement test, and that the functions of 

 digjestion would in such a case be carried on outside the test of 

 the animal. 



Psammosphsera fusca presents at least two definite and constant 

 varieties : var. parva (Flint) and var. testacea (Flint) (i.?). In the 

 former of these varieties — parva — the test, which is always of com- 

 paratively small dimensions, is neatly symmetrical and spherical, 

 composed of small sand-grains rigidly cemented together, without 

 definite aperture of any kind C PI ate II, fig. 7), and very often 

 around a sponge-spicule which projects on opposite sides of the 

 sphere, sometimes to a length many times exceeding the total dia- 

 meter of the test. This spicular form, figured by Brady in his 

 ^ Challenger' Eeport (J), but unaccompanied by any descriptive 

 diagnosis, is of very infrequent occurrence, and is, in our experience, 

 extremely local (Plate II, fig. 8). As will be seen by reference to 

 our Table, Psammosph^ra fusca occurs in no less than 85 stations 

 out of the 145 stations examined and analysed. At most of these 

 stations sponge-spicules form a constant and common feature 

 of the sea-bottom. At many of the stations these spicules form a 

 large percentage of the available building material, but the spicu- 

 liferous PsavimospJiwra fusca var. parva occurs only at two 

 stations, at only one of which more than an occasional specimen 

 is ever to be found. The one exception is Haul 228, taken off 

 Feb, 19th, 1913 C 



