A SIEVE-LIKE MEMBRANE IN LEUCOSOLENIA. 269 
preserved specimens it is a matter of great difficulty to make out 
satisfactorily the structure of the ectodermal epithelium.” In 
carefully prepared sections “the ectoderm generally appears... 
as a delicate but sharp outline, with a moniliform or beaded 
appearance, due to the swelling caused by the presence of the 
nucleus in the centre of each cell.” The author then figures 
and describes the ectoderm in Leucosolenia Wilsoni, 
n. sp. I never saw such distinct cells in L. coriacea, but I 
have already expressed my opinion above that the structure of 
the ectoderm varies at different ages. The collar-cells figured 
by the author from Leucosolenia proxima on pl. viii, figs. 
3 and 4, are unlike any I have seen in L. coriacea, but it is 
possible that they vary in shape in different species. The 
mesodermal network described by the author in the gastral 
cavities of L. proxima and Wilsoni (p. 13, pl. viii, figs. 
1 and 2) is very remarkable, and reminds one at first sight of 
the sieve membrane described here; but from the description 
of the network there can be no real comparison between it and 
my sieve membrane. 
In his “ Preliminary Account of Synute pulchella, a 
New Genus and Species of Calcareous Sponges” (Dendy, 
‘Proceedings of the Royal Society of Victoria,’ March 12th, 
1891), the author mentions that “each gastral cavity has also 
a single large well-developed diaphragm situate just within the 
osculum’”’ (p. 3). As far as one can judge from the descrip- 
tion, this diaphragm may well be homologous with my sieve 
membrane in Leucosolenia coriacea. 
List oF WORKS CITED. 
BowERBANK.—‘ Monograph of British Spongiade.’ 
BurtscH11.— Protozoa,” in ‘Bronn’s Klassen und Ordnungen des Thier- 
reich’s,’ i. 
1. Denpy.—“ Studies on the Comparative Anatomy of Sponges,” IV: “On 
the Flagellated Chambers and Ova of Halichondria panicea,” 
_ Quart. Journ. Micr. Sci.,’ Jan., 1891. 
2. Denpy.—‘ Monograph of the Victorian Sponges,” Part I; “The Organ- 
