OXNERELLA M A ULTIMA. 
517 
central granule, all the protoplasm of the body is usually 
closely packed with ingested food-bodies (PL 27, fig. 1). The 
protoplasm itself is colourless. There is no obvious differen- 
tiation of the cytoplasm into ectoplasm and endoplasm. 
There is no contractile vacuole, no stalk, and no spicular 
skeleton, either external or internal ; nor is a gelatinous 
investment present. 
There is a single relatively large nucleus (PI. 27, figs. 1, 2), 
which is vesicular, with a large central karyosome. The 
nucleus is excentrically placed, and usually ovoid, its more 
pointed end being directed towards the centre of the organism 
(PI. 27, figs. 1, 2). Those pseudopodial axes which lie in 
contact with the nuclear membrane often stain more deeply 
than the rest, and thus appear as dark lines traversing the 
surface of the nucleus. (This can be seen in the nucleus 
shown in PL 27, fig. 7.) 
Most specimens are not perfectly spherical, and the in- 
gested food-bodies often project above the surface of the 
body, giving it an irregular contour. It is thus impossible to 
measure the diameter of most individuals with great accuracy. 
The diameter of fifty fixed and stained specimens (all nearly 
spherical, and not dividing), measured as nearly as possible, 
showed a range from about 10 fi to 22 /u , the mean being- 
about 14 fi. 
2. Systematic Position. 
From the foregoing brief account of the structure of this 
heliozoon, it will be clear that it belongs to the group of 
naked forms (such as Actinosphaerium, etc.) which con- 
stitute the order Aphrothoraca of R. Hertwig. Schaudinn 
(1896) enumerates nine genera in this order, which all differ 
in important particulars from the present form. Actino- 
lophus, Zooteira, and Wagnerella (= Haeckelina) 
are stalked; Actinosphaerium and Gymnosphaera aro 
multinucleate, and possess sharply differentiated ectoplasm 
and endoplasm ; Actinophrys is uninucleate, but possesses 
