Development of the Marine Sponges. 405 



embryo swims ; i, arrow showing the direction in which the 

 body rotates. 



N.B. The arrows in this figure also represent the directions 

 of progress and rotation respectively in the embryos of Halisarca 

 lobularis and Grantia compressa. 



Fig. 22. The same, active locomotive embryo a day or two after issuing 

 from the parent, showing the shortening and widening which 

 take place previous to its becoming stationary ; also the more 

 general form of the brownish-yellow mass of root-cells (a), and 

 an eccentric position of the papilla at the apex (b). Other detail 

 the same as in the foregoing figure. 



Fig. 23. The same, vertical section of the ampullaceous sac of adult, 

 showing its globular form and the position of its pavimental 

 lining of monociliated spongozoa : «, separate spongozoon. 



Fig. 24. The same, specimen of the spicule of adult. 



Fig. 25. Esperia cegagropila, Cart, (variety, see p. 3.33. Loc. Budleigh- 

 Salterton), spheroidal form of embryo, obtained by forcible ex- 

 pulsion from the parent, showing that it is encapsuled, ciliated, 

 and composed internally of sarcode charged with cells of dif- 

 ferent sizes, granules, and all the forms of spicules peculiar 

 to the species : a, cells bearing cellulee ; b, skeleton-spicules ; 

 c, d, e, forms of flesh-spicnles respectively, viz. anchorate, bi- 

 hainate, and tricurvate ; /, monociliated layer of the surface 

 or ectoderm ; g, capsule. 



Fig. 26. The same, tricurvate spicule from the substance of the adult, 

 showing its linear, almost straight form, and entire enclosure in 

 a mother cell : a, spicule ; b, mother cell ; c, nucleus of cell. 



Fig. 27. Microciona armata, Bk. (?) (see description p. 457), tricurvate 

 spicule, curved suddenly in the centre, elongated at the ends 

 which are spined : a, spicule ; b, mother cell ; c, nucleus ; d, more 

 magnified view of spined extremity. 



Plate XXII. 



N.B. All the figures in this Plate, with the exception of the last, 

 are drawn to the scale of I-12th to l-830th of an inch — that is, to a scale 

 a little less than half the size of the foregoing. 



Fig. 28. Halichondria simulans, embryo at the commencement of the 

 fourth period of development, showing that it has become 

 fixed and attached by the posterior extremity to the surface of 

 the pebble ; the body somewhat contracted, and the cilia of the 

 ectodermal cells withdrawn, while those forming a ring round 

 the base are still moving languidly : a, body ; b, papillary emi- 

 nence at the apex ; c. ring of large cilia and expanded base (the 

 latter formed by the root-cells ?) ; d, surface of pebble ; e, posi- 

 tion of the spicules in the embryo. 



Fig. 29. The same, more advanced stage, showing the expansion of the 

 ectoderm laterally into a kind of denticulated foot (a a), and 

 the opaque body (b) in the centre erect and conical, with the 

 papilla, now become a depression, at the apex (c). Lateral view. 



Fig. 30. The same, still more advanced stage, showing that the smooth 

 surface has become monticular or angulated (a), and the aperture 

 of the vent or osculum more prominent and excavated (b). 

 Upper view. 



Fig. 31. The same, embryo, lateral view, but with the foot a little 

 retracted. 

 Ann. & Mag. N. Hist. Ser. 4. Vol. xiv. 29 



