399 



naked eye; these granules are very minute irregular rosettes, about 

 10 jjL in diameter. Anchors, from 200 — 250 ji, long, straight or slightly 

 arched inward, with smooth arms; a few small blunt teeth on the 

 vertex; arms not in the same plane as shaft but bent outward; poste- 

 rior end broadened out to form a short notched or branched bow, with 

 numerous hne pointed teeth. Plates from 130 — 140 [x long and about 

 1 1 p. broad ; edges smooth ; six anterior holes large, with about 1 4 

 coarse blunt teeth; seventh large hole, with about four blunt teeth on 

 its anterior margin, somewhat pointed behind; medium sized hole on 

 each side of this and three small ones back of it, all with smooth 

 edges. External side of the plate with a bow, which starting from the 

 outer edge of the medium sized smooth holes, bends outwards and 

 forwards, bearing a few teeth on its anterior border. All these calca- 

 reous particles are very much like those figured by Théel for Stjnapta 

 fida (Challenger Report, Vol. XIV, Part XXXIX, Plate I Fig. 9). 

 But there are in addition, small straight or curved rods about 200 p- 

 long which may be perfectly smooth, somewhat knobbed or enlarged 

 and rough at the ends; more rarely slightly forked or branched. These 

 rods occur only in the tentacles, chiefly at the tip, and they seem to 

 be more abundant in young than in old Synapta. They lie parallel to 

 the long axis of the tentacle or if in a digit, parallel to its long axis. 

 Development: Eggs unusually large, about 210 jjl in diameter, 

 light yellow in color. They are set free in the body cavity of the adult, 

 but whether self-fertilization takes place or not, I have been unable 

 to determine. Artificial fertilization never succeeded no matter whether 

 the ova and spermatozoa came from the same or different animals. 

 Ripe sperm and apparently ripe ova occur at the same time in the same 

 individual. Segmentation is total and equal. No polar bodies were found 

 altho looked for carefully. Segmenting eggs are surrounded by a deli- 

 cate vitelline membrane, probably formed as a result of fertilization, 

 as it is wanting in unfertilized eggs. At the 16-cell stage, the embryo 

 appears as a ring or band, two cells Avide and eight cells in circumfer- 

 ence, surrounding a cavity which is cylindrical instead of spherical 

 and open at both ends. The 32-cell embryo is arranged in four series 

 of eight cells each ; the upper- and lowermost of these series have a 

 less diameter than the t\Vo middle series and accordingly the embryo 

 begins to assume the spherical form, altho the sphere is still open at 

 the poles. Subsequent divisions close these openings and form the 

 complete blastula. Invagination takes place and the gastrula devel- 

 ops as shown by Selenka for S. digitata. The gastrula is well cover- 

 ed with cilia and soon escapes from the egg-membrane. It is very 

 active and swims about freely in the body cavity of the mother. Devel- 



