ANATOMY, EMBRYOLOGY, PHYSIOLOGY, BIOLOGY. SjpOlig. 15 
The flattened epithelium of Calcarea (p. 398) perhaps has flngellq,, but 
not more than one to each cell. For the mesoderm the term “inter- 
mediate layer” (Zwischenschicht) is proposed (p. 398). It contains : (1) 
amoeboid cells (p. 399), which function as phagocytes aud are also the 
mother cells of the ova and spermatozoa ; (2) stellate and fibrous cells 
(pp. 400 & 401 ; in Ascetta primordialis, p. 198, A. clathrus, p. 211, 
Sycandra raphanus, pp. 252 & 253, S. setosa , p. 259). The deeper lying 
cells have numerous processes, which become more tangentially directed 
the nearer they approach the surface, at the same time decreasing in 
number, until immediately under the epithelium they become bipolar 
fibre cells, which form sphincters ; in the gastral membrane of Sycandra 
setosa they are numerous. All these cells and their processes are con- 
tractile, and bring about the closure of the pores and oscula. (3) Sense 
cells (p. 402). Some spindle-shaped, with several root-like processes at 
the inner end, others multipolar, with a centrifugally directed process, 
others rounded or multipolar without differentiated processes. For a 
probably nervous “ synocil ” like structure in Sycandra raphanus , see 
p. 251. For strongly staining cells of irregularly rounded shape, pro- 
bably nervous, situated near the pores, in Grantia capillosa , see p. 278. 
(4) Skeleton forming cells (p. 403). The spicules arise in irregularly 
shaped cells. In Ascetta primordialis (p. 199) the author finds, in con- 
tradiction to Metschnikoff, that the young spicule forming cells are clear, 
and more or less free from granules. The growing spicule becomes sur- 
rounded by granular flattened cells with processes, placed singly or in 
groups. These cells, however, are rarely to be found on the spicule, and 
appear to vanish as soon as the spicule has attained its full growth. 
(5) Glaud cells. Multipolar elements which are probably such, occur 
under the epithelium of the oscular crown in Sycandra raphanus. (6) 
Ova (p. 404). For description of ova, with what appeared to be polar 
bodies, in Ascetta primordialis , see p. 209. Ova in Sycandra raphanus, 
p. 255 ; in S. setosa , p. 259 ; in Vosmacria corticata ) p. 299. (7) Sperma 
(p. 404). 
The author considers that there is no essential difference between 
triaetine and tetractine spicules, and hence unites such of Haeckel's 
genera as are only distinguished by the possession of these two kinds of 
spicules. It is doubtful if the triactines are the most primitive kind of 
spicule, since many simple Ascons have only rhabds. The origin of 
rhabds is very doubtful ; either they have arisen independently, or from 
triactines, or from tetractines. Perhaps they have arisen in different 
ways in different Sponges. 
Sponges are to be looked upon as a phylum of Metazoa belonging to 
the grade Ccelentera, but not on that account phylogenetically related to 
Onidaria. They are Ccelcntera traversed by a canal system, with endo- 
dermal collar cells and with their skeletal, sexual, and muscular cells 
formed in the “ Zwischenschicht ” and not of epithelial origin, without 
nettle-cells and moveable appendages. In Sponges an “individual” can 
have any number of oscula. No scientific conception of individuality 
