40 GEORGE BIDDER. 
20. Drenpy, A.—1893, ‘Quart. Journ. Mier. Sci.,’ vol. xxxv, p. 159. 
21. Maas, O.—1893, ‘Z. Jahrb. Morph. Abth.,’ Bd. vii, p. 331. 
22. Franzb, R. H.—1893, ‘Zool. Anz.,’ xvi, p. 44. 
23. Mastrermay, A. T.—1894, ‘ Annals and Mag. Nat. Hist.,’ vol. xiii, p. 485 
24, Torsent, E.—1894, ‘ Arch. Zool. Exp.,’ vol. ii, p. 283. 
25. Scuaupiny, F.—1894, ‘ Sitz. Akad. Wiss.,’ Berlin, lii, p. 1277. 
EXPLANATION OF PLATE 2, 
Illustrating Mr. G. Bidder’s paper on “The Collar-cells of 
Heteroceela.”’ 
Figs. 1 to 14 and fig. 19 are from living cells. All the drawings except 
figs. 3 and 21 are multiplied about 1000 times linear; figs. 1, 2, 15, 16, 17, 
18, 19, and 20 being drawn with the camera lucida,} figs. 9, 11 ce, 12, and 22 
drawn free-hand and scaled from micrometer measurements, the remaining 
figures are free-hand drawings approximately to the same scale. All drawings 
were made with Leitz =, oil-immersion, Zeiss oc. 3 old system, rarely oc. 4. 
Figs. 3 and 11 are from Sycon raphanus, fig. 21 from Leucandra 
aspera, fig. 22 from Acanthella pulcherrima, the remainder from 8. 
compressum, 
Fic. 1.—Drawn from living 8. compressum, forty minutes after it was 
taken froma tide-pool. These collar-cells were pressed against the cover-slip, 
hence they appear closer together and more in one place than in the other 
figures. Cf. fig. 15. 
Fie, 2.—Another part of the same sponge, drawn immediately after the 
section was placed on the slide. The flagella were so active that only their 
bases could be drawn. 
Fie. 3.—S. raphanus, living collar-cells (Naples, 1889), prob. x 2500. 
The shaded spherules were stained with Bismarck brown; the full number is 
not drawn in all the cells. 
Fic. 4.—T wo cells with distal globules (excreta ?), alive, flagella very active; 
from 8. compressum two anda half hours exposed by the low tide, two 
’ The small numerals at the side of fig. 16 show the distortion found to 
exist in drawing with the Nachet camera when all adjustments are made with 
apparent accuracy. 
