304 WILSON. [Von. TX. 
The two mesodermic processes, m. ~., do not come to an 
abrupt end, but die out imperceptibly. The ectodermal mem- 
brane, from the very beginning of its appearance, becomes 
covered with débrzs, much of which is organic. In Fig. 54, 
round the main body of the sponge are strewn little masses of 
degenerating cells, dead protozoa, and homogeneous, rounded 
masses which betray their organic nature only by their affinity 
for the stain, and which are evidently degeneration products. 
A good part of this débris looks as if it came from the sponge 
itself, as if it were composed of cells which had lost their 
connection with the sponge in some way, and then degenerated. 
Before completing the description of the ectodermal membrane, 
Pl. XVIII, Fig. 57, needs a word of explanation. The sponge 
was surrounded by an ectodermal membrane of average width, 
which in the region drawn was thrown, perhaps artificially, 
into a fold, x, close to the edge of the mes-entoderm. 
My description of the peripheral region of the young sponge 
differs from that given by Maas for Spongilla (14), which he 
finds can also be applied to the case of Esperia (16). In the 
accuracy of my own observations as far as they go, I am 
confident ; and those of Maas seem to have been made with 
such care that I am inclined to believe farther study will 
reconcile the two descriptions. 
In the young Spongilla, Maas observed that the whole 
periphery becomes amoeboid. The formation of processes was 
followed in the living sponge, and it could be seen that a 
hyaline prolongation was thrown out far beyond the inner 
tissues, into which the inner cells slowly flowed, the outline 
then becoming more even. To this outer region, which is in 
constant motion, Maas gives the name of ‘der amoeboide 
Hof.” The amoeboid ‘‘Hof” forms the peripheral zone of 
the sponge, and is composed of ectoderm. Internal to it is 
the body of the sponge, z.¢.,the mass of mes-entoderm. The 
movements of the amoeboid “ Hof” are due to the amoeboid 
movements of its constituent (ectoderm) cells. Silver nitrate 
preparations show that the cells at the extreme edge of the 
Hof are in active motion, throwing out pseudopodia, and com- 
bining to form lobes (the hyaline prolongations, the formation 
