DEVELOPMENT OF BOLOCERA 585 
SUMMARY AND CHRONOLOGY. 
Egg large, floating ; maturation prior to shedding ; fertiliza- 
tion external; at least twenty-four nuclei present before 
cleavage of egg-mass takes place (fifteen hours); cleavage 
total leaving a small central cavity ; the inner ends of the 
cells separate off to form a central trophenchyme (twenty-four 
hours); a greatly-folded ‘ preblastula’ stage during which 
groups of cells are included in the trophenchyme (forty-eight 
hours) ; the blastula becomes more or less smooth and spherical 
(three to three and a half days) ; gastrulation begins (four to 
five days); gastrulation complete and first mesogloea formed 
(six and a half to seven and a half days), the trophenchyme 
passing into the archenteron, and degeneration of its nuclei 
taking place; blastopore narrows and virtually closes, involu- 
tion of stomodaeum taking place; larva elongates (nme to 
ten days); sulco-lateral mesenteries begin to form (fifteen 
days) ; aboral end shows cement gland formation, and rudi- 
ments of the other mesenteries appear (twenty days) ; fixation 
and shortening of the larva (twenty-five days); formation 
of four additional mesenteries (thirty-six days); complete 
absorption of trophenchyme within archenteron (thirty-six 
days). For cilia, movements, &¢., see p. 582. At no stage is 
there a tuft of specially elongated aboral cilia. 
REFERENCES, 
1. Appellof, A.—‘‘ Studien itiber Aktinien-Entwickelung”’, ‘ Bergens 
Museum Aarbog’, 1900, pp. 1-99. 
2. Carlgren, O.—“ Beitrage zur Kenntniss der Aktiniengattung Bolo- 
cera ’’, ‘ Oef. Vet. Akad. Forh. Stockholm ’, vol. 48, 1891, pp. 241- 
50. 
3. “Die Aktiniarien der Olga-Expedition ”, ‘ Wiss. Meeres-Unter- 
such, (Helgoland) ’, Bd. V, pp. 33-55. 
4. ‘Studien tiber Nordische Aktinien”’, ‘K. Svenska Vet.-Akad. 
Handl.’ 25, no. 10, 1893. 
5. Cary, L. R.—‘“ The Formation of the Germ Layers in Actinia 
bermudensis, Verr”’, ‘ Biol. Bull. Woods Hole’, xix, 1910, 
p. 339-46. 
6. Delage et Hérouard.—‘ Traité de Zoologie concréte ’, ii. 2, Coelenterés. 
7. Faurot, L.—‘‘ Etudes sur l’anatomie, Vhistologie, et le développe- 
