EXPLANATION OF PLATE II. 



All the figiires are drawn with an ordinai'y Nachet camera and projected 

 on the working table. We realize perfectly well that such drawings are 

 subject to faults. But these are equal for all the figures and for our purpose 

 camera faults are of no influence in the least. As for general niethods of 

 preservation , see IV in the letterpress. For the drawings we used always 

 eye-piece n°. 42 the figures thus being magnified 1600 times. In the figures 

 taken from sections (flgs. i — 4 and 7) the thin line uniting the bases of the 

 choanocytes represents the outline of the chamber. The open spaces are places 

 where choanocytes ware lying, which were cut, being partly out oftheplane 

 of section. We therefore did not draw those cells. For the rest is all drawn 

 with great care and representing nothing more than was actually seen. ; the 

 borders of the collars are printed a little too sharp. 



Figs. 1 — 6. Spongilla laciistris. 



1. Section of a flagellated chamber; ap. apopyle. 



2. id. a two choanocytes, b. coUar and flagellum of one of the opposite side. 



3. id. Three cells seen from the side; in the centre of the chamber three 

 sections of collars with their flagella. 



4. id. In none of these four figures is any tracé of a inembrane uniting 

 the collars, nor do the later ever touch each other. 



5 and 6. Isolated choanocytes, showing the most perfect, smooth collars, 

 without any rest of some Sollas's membrane. The black spots are milk 

 globules, the sponge having been for five quarters of an hour in milk 

 water. About the vacuoles near the base of the flagellum, the ring at 

 the base of the collar and the differences between them and the choano- 

 cytes of Halichondria we must refei' to our next paper. 



Figs. 7 and 8. Halichondria panicea, 



7. Section of flagellated chamber, showing that there is no tracé of Sollas' 

 membrane. 



8, Isolated choanocyte. 



