32 Proceedings of the Royal Physical Society. 
4. On Salpistes (Stentor) Mulleri and castaneus. (Fig. 11.) 
In the last edition of Pritchard's "Infusorial Animalcules" 
it is stated that Stentor Mulleri, " when kept long in glass 
vessels, fasten themselves to the sides, form a slimy covering 
around them, and die ;" and, further, that Ehrenberg had re- 
marked that " thej would gradually congregate, select some 
particular spot, and then attach themselves, evincing, as it 
were, not only a degree of sociality, but a mental activity." 
In their apprehension of these facts I believe the authors 
above quoted to be mistaken. It is well known that many 
aquatic animals have the power of secreting masses of viscid 
gelatinous matter, which does not readily undergo decomposi- 
tion, to serve as a nidus for the protection of their ova. Thus 
the nudibranchiate and other molluscs deposit on stones and 
weeds long convoluted ribbons of clear firm jelly filled with 
their eggs, which remain therein until hatched. Many in- 
sects, aquatic in their earlier stages of existence, adopt the 
same mode of protecting their young. In the genera Sertu- 
laria, Plumularia, Campanularia, and Laomedea, species 
also are found in which the young undergo partial develop- 
ment whilst still contained in gelatinous cases attached to the 
exterior of the reproductive cells, as I have already described 
to the Society in the case of Laomedea lacerata. Other 
animals employ the same matter to form envelopes or loricse, 
into which they can retire protected from harm. In this w^ay 
is formed the " house" of Appendicularia flabellum, of which 
Mertens has given so marvellous an account, mistaking it for 
a respiratory organ. Amongst the Rotiferae we find Stephano- 
ceros, FlosGularia, Limnias, Melicerta, and others, each liv- 
ing privately in its solitary abode, formed either of clear gela- 
tine, or of the same substance strengthened with mud or other 
extraneous matters ; while in the genus Oonchilos a colony 
of animals unite their efi'orts to form a transparent globe, 
which is rapidly rolled through the water by a multitude of 
living wheels. Descending to the Protozoa, we may see 
Ophrydium versatile, an animal scarcely visible to the unas- 
sisted eye, attaching itself to our tanks by its little speck of 
