A SIEVE-LIKE MEMBRANE IN LEUCOSOLENIA. 261 
prove absolutely a true homology between the two structures. 
I should prefer to look upon them as “ homoplastic”’ merely ; 
as agreeing in anatomical relations, and perhaps also in their de- 
velopment and mode of origin, but not as genetically connected. 
In Calcarea I know of no structure which can be strictly 
homologised with this membrane, though I think it probable 
that the “ Mundhaut” described by Haeckel, as well as the 
oscular sphincters, not unfrequent in Calcarea, may be so 
homologous. Here in Naples I have examined very carefully, 
by various methods, numerous oscula of Leucosolenia pri- 
mordialis, but can find no trace of anything resembling the 
sieve membrane of Leucosolenia coriacea; neither could I 
in Leucosolenia botryoides. 
There is another point about this membrane which is not 
without importance. ULeucosolenia coriacea is a sponge 
which usually occurs totally devoid of oscula.1 In Bower- 
bank’s ‘ Monograph of British Spongiade,’ vol. ii, p. 35, we 
read, “‘ Dr. Johnston in treating of this sponge says, ‘ There 
are no fecal orifices.’ I have carefully examined a consider- 
able number of specimens with a microscopic power of 160, 
but have been unable to detect any of the mouths of the 
cloaca, and attribute this failure to the habit of the animal of 
closing these orifices at the approach of danger, or while in a 
state of inaction; and the total absence of internal defensive 
spicula would seem to indicate the existence of such a power 
for its protection from its enemies.’ Haeckel (‘ Kalk- 
schwamme,’ vol. ii, p. 25) writes, ‘‘ Die bisherigen Beobachter 
dieses Kalkschwammes haben allerdings fast ausnahmslos nur 
eine Hauptform derselben beschrieben, namlich den mund- 
losen Stock (Auloplegma coriaceum, figs. 27—33).” This 
“‘lipostomy ”” is of common occurrence in many sponges, and 
according to Haeckel is always found in some Calcarea, e. g. 
1 Ciard found’ at Wimereux Tarrus, Auloplegma, and Ascometra 
forms; see ‘ Bull. Scient. de France et de la Belgique, xxii (1890), part 1, 
p. 70. But Topsent (‘Contributions a l’étude des Clionides,” ‘ Arch. de 
Zool. expér. et gén.,’ v bis, mém. iv) found at Luc only Auloplegma 
forms. 
