TRANSACTIONS 



OF 



THE ZOOLOGICAL SOCIETY 



OF LONDON. 



I. The Development of the Starfish Solaster endeca Forbes. By James F. Gemmill, 

 M.A., M.D., D.Sc, F.Z.S., Lecturer in Embryology, Glasgow University, and in 

 Zoology, Glasgow Provincial Training College. 



(Received and read November 29, 1910.) 



[Plates I.-V.] 



Contents. 



Page 

 I. Steucitjkb and Position 3 



II. OVAEIES AND OvA 4 



Arrangement and structure of the egg-tubes, 4 ; muscular tissue and sinus-spaces in 

 their walls, 4 ; relation of the latter to genital sinuses and haemal tissue, 5 ; growth 

 of the ova, 6 ; accumulation of yolk-granules, 6 ; yolk-nnolei, 7 ; follicle-cells, 7 ; 

 egg-ducts, 8. 



III. Matttkation, Spawning, Fektilization, &c 9 



Time of maturation, 9 ; season, &c. of spawning, 9 ; the ova in water, 10; membrane of 

 fertilisation, 11 ; cross-fertilisation, 11 ; early and later segmentation, 11 ; formation 

 of blastula by egression and of gastrula by invagination, 12; appearance of cilia, 12; 

 movements of blastula and gastrula, 13 ; hypenchyme, 13 ; chronology, 13. 



IV. ExTBENAt Chaeactbes, Movbmbnts, &c. riTEiNa the Free-swimming Period 14 



Elongation of gastrula, 14 ; formation of arms and of sucker, 14 ; preoral lobe and body of 

 larva, 14 ; formation of hydropore, 14 ; closure of blastopore, 1.5 ; movements of the 

 larvae, 15 ; ciliation at anterior and posterior ends and over general surface, 15 ; 

 commencement of fle.xion and torsion of the preoral lobe, 16 ; first appearance extern- 

 ally of hydrocoele lobes and of aboral arm rudiments, 17 ; chronology, 17. 



VOL. XX. — PART T. No. 1. — February, 1912. b 



