486 E. A. MINCHIN. 
derm externally and endoderm internally. I see as yet no 
reason why I should depart from that opinion. On the other 
hand, it can hardly be doubted that the sphincter here described 
arises as a simple ingrowth of ectoderm, and consists of this 
layer only on both faces. In the young forms the sphincter 
shows only one or two cells on either face in transverse sec- 
tion (fig. 7, a, 6, c), while in the older ones it consists ofa 
great number lying side by side (figs. 7 a, 8, 11, 12, 13), so 
that it evidently grows with the osculum. I have not yet 
found an osculum devoid of asphincter, but it is very probable 
that the young Olynthus would have none.' 
In specimens of this sponge fresh from the sea the oscula 
were, as I have said, exceedingly conspicuous.? How is it 
these oscula have not been found before? I selected on my 
first collecting trip several large specimens of the sponge with 
widely open oscula, and put them into a separate vessel in sea 
water. What was my astonishment, however, when I got 
back to the Zoological Station, to find no trace of osculain any 
of my specimens, not even an elevation to mark where they 
had been! The thin delicate walls of the sponge had com- 
pletely collapsed, and the whole presented a shrivelled appear- 
ance, as different from the beautiful outlines and transparent 
yellow colour of the fresh living sponge as anything could be 
imagined. Ona second occasion I selected another very fine 
specimen, and put it in a separate vessel, and brought it back 
with great care, changing the water several times on the way 
home. It was, however, of no avail; it arrived in the same 
shrivelled condition. The only indication that these sponges 
1 Since Haeckel observed only Clistolynthus forms it is possible that even 
the Olynthus has a sphincter. On the other hand, it would be quite possible 
for an Olynthus to contract itself completely without any special sphincter. 
Vide Metschnikoff’s figure of a Clistolynthus of Ascetta blanca in longi- 
tudinal section, ‘ Zeitschr. f. wiss. Zool.,’ xxxii, 1878-9, Taf. xxii, fig. 9. 
2 T cannot but express my astonishment that Haeckel did not see them, 
since he tells us in his monograph (p. 33) that he found this sponge growing 
in great quantities in a little bay (San Clemente) on the south side of the 
Spalmadori Cliffs on the coast of Lesina in 1871, and collected in a short time 
several hundred small and large colonies. 
