12 8-pong . 
SPONGIjE. 
pressure (fig. 5). The internal mass (2) is believed by the author to 
represent a supply of food enabling the larva to wander for a long dis- 
tance without becoming fixed, and to have nothing to do with mesoderm, 
which arose much earlier, and though hidden by the later-formed food- 
yolk, is doubtless still there, giving rise to the spicules observed by 
Metschnikoff. 
Maas describes the development of the freshwater Sponge. The 
ovum is full of yolk granules. The segmentation, which takes place 
within the maternal follicle, is total and regular, leading to the formation 
of a morula of about sixty-four cells. The internal cavity of the embryo 
arises as a sinking-in at one pole of the morula, when its cells are still 
similar in structure to the ovum. Rapid cell division, accompanied by 
differentiation of the tissues, then takes place. The peripheral cells of 
the embryo become columnar ectoderm cells, arranged in an epithelium. 
The cavity of the embryo is lined by a distinct layer of cubical endoderm 
cells, heaped together in some places, and in others sending pro- 
cesses into the inner mass of mesoderm cells, to form the rudiments 
of the flagellated chambers. The mesoderm consists of (1) large 
cells still containing yolk ; (2) cells without yolk, resembling later 
connective tissue cells ; (3) scleroblasts. As the embryo grows, (1) 
gradually disappear, and the ground substance appears, perhaps 
secreted intracellularly. The flagellated chambers arise by further dif- 
ferentiation of the endoderm cells lining the cavity. The ectoderm cells 
acquire flagella, and the larva is set free. It swims with the pole of the 
cavity directed forwards. It has a well-differentiated mesoderm, and 
flagellated chambers lined by collar cells opening into the central cavity, 
but there are no pores or oscula. 
The larva fixes by the pole of the cavity, and becomes flattened out 
into a crust. The ectoderm colls flatten out and lose their flagella, and 
then become amoeboid, and throw out pseudopodia at the margins of 
the Sponge, but still remain perfectly continuous, with the general ecto- 
derm covering all the tissues and the spicules. The play of the pseu- 
dopodia gradually ceases, and at the same time the inhalent canals arise by 
dipping of the ectoderm to meet the flagellated chambers, which have been 
brought near the surface by the flattening of the Sponge. The osculum 
arises as a breaking through of the primitive cavity of the embryo to 
the interior. The primitive oavity becomes the exhalent system, 
Tobsent (6) describes in Cliona vastifica a method of reproduction by 
means of gemmules (p. 52). The author also has observations on the 
embryos of Reniera rosea (pp. 99, et seq.), R. simulans (p. 104), Amor- 
phina panicea (p. 112), Dendoryx dujardini (pp. 116, et seq,). In Reniera 
the embryos acquire, before the appearance of the cilia, a cap of pigment 
at one pole, which is wanting in the embryos of the genera Amorphina and 
Dendoryx. In the appendix, the author notes the breeding season of many 
of the Sponges to be found at the zoological station of Luc, and gives a 
list of the Sponges which set free their embryos in each month from June 
to October inclusive. 
