10 Spong. 
SPONGI/K. 
Endothelial cells, lining embryo-containing cavities and the spicule rays 
which project into the gastral cavity ; in the latter case the cells may bo 
endodermal. (5) Reproductive cells : the ova arise from (2) ; they are 
oval in form, with distinct nuclei, and round them are congregated (in 
the young ova of L. cavata) a number of mesodermal cells, which are 
probably the commencement of the characteristic capsule. The nucleus 
(in L. pelliculata) has one very large spherical nucleolus and a distinct 
membrane. In L. depressa there is an irregular row of spherical granules 
just inside the nuclear membrane, which resemble the granules of the 
protoplasm outside. 
In L. cavata a number of yellow granules, arranged in clusters, each 
with a dark spot (nucleus ?) in the centre, lie embedded in largo numbers 
at fairly regular intervals in the mesoderm beneath the collared cells. It 
is doubtful if they belong to the Sponge body, or are symbiotic alga. 
The skeleton consists of triradiate, quadriradiate, and oxeote spicules. 
The canal system serves for division of the genus Leucosolenia into 
three sections : — I. Simplicia , including Olynthus types, which never 
form colonies, and also colonial forms, in which the whole colony 
consists of individuals (Ascon persons) which may branch, but which 
never form complex anastomoses nor give off radial tubes, so that the 
individuality of the different members of the colony is always recog- 
nizable. II. Reticulata , in which the Sponge colony forms a more or 
less complex network of branching and anastomosing tubes ; and it is 
no longer possible to distinguish the individual Ascon persons of which 
the colony is composed. The gastral cavities of the Ascon tubes may 
retain the primitive hollow condition, there being no ingrowth of the 
mesoderm or ectoderm (Subsection 1, Indivisa ), or may be more or less 
subdivided into incomplete chambers by ingrowths of mesoderm, or of 
both mesoderm and endodcrm (Subsection 2, Subdivisa), ill. Radiata. 
The Sponge consists of a single central Ascon tube, from which smaller 
tubes are budded off radially. 
The author has observed no species of Leucosolenia without an 
osculum, and thinks that in Auloplegma forms the oscula have been over- 
looked. 
Caual system of Leucosolenia lucasi , pp. 24 & 25, of L. stolonifer, pp. 
25 & 20, of L. dubia, p. 28, of L. stipitata, p. 28, of L. imlclierrima, pp. 
28 & 29, of L. cavata (reversed type of canal system), pp. 29 & 30, of 
L. ventricosa, pp. 30-32, of L. proximo , p. 33, of L. wilsoni ) p. 34, and of 
L. tripodifera , pp. 35-37. 
Keller (1) describes the anatomy of the Oligoceratina and Tetracti- 
nellida. In the skeleton of the Oligoceratina spongin is absent in the 
families Tethyadce } Chondrosidce , and Placospongidcc y but appears in the 
Spirastrellidce } allies of the last-named family j thus S. decumbens covers 
the surface on which it grows with a thin plate of spongin, from which 
arise vertical spongin lamellae. In Suberitidce spongin as a rule is 
wanting, but sometimes present ; in S. incrustans there is a network of 
fibre of stratified structure. In Renieridce spongin ps sparing and colour- 
