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B. W. PRIEST ON THE CALCAREA. 103 



blastula, the cells of which are partly converted into flagellated 

 cells, while a few at the base become granular, and produce the 

 larger rounded cells. It has now become a free swimming larva, 

 and passes from the parent sponge by the canals and out at the 

 oscula. After some little time the flagellated cells become 

 gradually withdrawn or invaginatedinto the hemisphere of granular 

 cells ; the central cavity of the amphiblastula is obliterated, and 

 replaced by another, surrounded by the flagellated cells. The 

 larva or embryo now consists of a sac, with a two-layered wall, 

 and a central cavity communicating with a mouth. After a while 

 it settles down on some foreign object, the outer granular cells 

 become the ectoderm, with its usual characters, the inner flagel- 

 lated cells, the endoderm, and the mesodermic layer appears 

 between the two. The embryo now lengthens, pores appear in its 

 sides, and an osculum opens at the free end, the original opening 

 bavins: become closed soon after the attachment of the larva. The 

 spicules now develop in the mesoderm, and it is a curious fact that 

 they have been seen in the embryo before leaving the parent, in 

 some cases. 



As before stated, the Asconidce are the simplest forms of the 

 calcareous sponges having a continuous flagellated endoderm, 

 Leucosolenia bottyoides being an example of this Family, and often 

 found on our coasts. Some very fine specimens were collected at 

 the Whitstable excursion of this Club last year (1886). It is 

 found parasitical on Alga5 and Zoophytes, and in general appear- 

 ance is arborescent, cylindrical, slightly pedicelled ; surface ap- 

 parently smooth, cloaca very large, armed internally with spiculated 

 equi-angular tri-radiate spicules ; spicular ray large and long, 

 slightly curved ; mouths of cloaca one or more, terminal simple, 

 and unarmed. Oscula and pores inconspicuous, spicules of skeleton 

 equi-angular, tri-radiate ; radii somewhat short and stout, rapidly 

 attenuating. Occurring, as this sponge does, in tufts, it might at 

 first sight be thought to be one complex sponge, but on careful 

 examination it will be found to be composed of numerous indivi- 

 duals clustered together. 



The Syconidce come next in order, having their walls pierced by 

 radial tubes, which tubes are lined by the flagellated collared 

 cells, and are only invaginations of the gastric wall, the latter thus 

 being covered with the pavement epithelium only, as occurs in the 

 ectoderm. 



