364 DISCOVERY REPORTS 



aborally (Fig. 50 b, c). After escape from the capsule the embryo assumes an elongated 

 form (Fig. 50 c) and the conspicuous folds of the surface disappear. 



T. spinata (Ridley) 



The first stage observed consists of a sub-spherical mass of spherical to polyhedral 

 cells of varying size, 0-03 5-0-07 mm. in diameter, the whole being 0-28 mm. long by 

 0-22 mm. across (Fig. 49 a). The subsequent histological changes resemble those of 

 T. charcoti and result in an oval embryo with a central mass of granular cells and an outer, 

 cortical layer of columnar cells (Fig. 49 b). The first spicules to appear are roughened 

 styli, 0-15 by 0-004 mm., followed by raphides measuring 0-07 mm. long. The sub- 

 sequent changes are similar to those found in T. charcoti (Figs. 49 c and d). 



T. massa, Ridley and Dendy 



A few large embryos (Fig. 51) were found in two specimens, all at about the same 

 stage of development, so that it is impossible to say much concerning the development 

 in this species. Two important features may, however, be noted: (i) the large size of the 

 embryos, and (ii) that the first spicules to appear are raphides, measuring 0-14 mm. 

 long. 



T. pectinicola, Thiele 



Although this species does not figure in the Discovery collections, drawings of embryos 

 found in the type specimen are included (Fig. 52 a-c) for the sake of comparison with 

 other species. 



Other species in which embryos were found are : 



Plakina monolopJia, Schulze. A specimen, collected on January 17, contains numerous 

 embryos in various stages of development. 



P. Irilopha, Schulze. One specimen collected on December 23 contains a few 

 ova; the second, collected on March 14, is filled with embryos in all stages of develop- 

 ment and a section of it presents the same appearance as that figured by Schulze (1877, 

 pi. iv, fig. 20) for Oscarella lobuloris (Schmidt). This is the first time the embryos of 

 Plakina trilopha have been recorded, and although Schulze has figured the develop- 

 mental stages of P. monolopha, which so far as they go do not differ from those of 

 P. trilopha, he omitted to record the date on which reproduction takes place. 



Haliclona bilamellata, sp.n. Two specimens, collected in April, contain scattered ova 

 or embryos in very early stages. 



Callyspongia flabellata, sp.n., collected in March, contains numerous oval embryos, 

 0-18 mm. in longest diameter. A few are aspiculous, but most of them contain oxea, 

 0-039-0-06 by 0-002 mm., which appear to arise as a tangential layer in the epiblast 

 and then to migrate inwards to form, finally, a compact mass at the centre of the embryo 



(Fig. 54)- 



Isodictya setifer (Topsent). A specimen, collected on March 21, contains eggs (or 

 young embryos?), spherical and with granular appearance, 0-087 i^"^- ^^ diameter. A 



