STUDIES ON THE EMBRYOLOGY OF THE SIPUNCULID^. 



451 



Hatschek, B. 



'80. Ueber Entwickelungeschichte von Echiurus und die systcmatische Stellung der Echiuridse (Gephyre 



chaetiferi). Arb. zool. Inst. Wien, Tom. 3, Heft 1, pp. 45-78, Taf. 4-6. 

 Hatschek, B. 



'83. Ueber Entwicklung von Sipunculus nudus. Arb. zool. Inst. Wien, Tom. 5, Heft 1, pp. 61-140, Taf. 4-9. 

 Mead, A. D. 



'97. The Early Development of Marine Annelids. Jour. Morph., vol. 13, no. 2, pp. 227-326, pis. 10-19. 

 Meisenheimer, J. 



:01. Entwicklungsgeschichte von Dreissensia polymorpha Pall. Zeit. wiss. Zool., Bd. 69, Heft 1, pp. 



1-137, Taf. 1-13. 

 Selenka, E. 



'75. Eifurchung und Larvenbildung von Phascolosoma elongatum Kef. Zeit. wiss. Zool., Bd. 25, Heft 4, 

 pp. 442-450, Taf. 29-30. 



EXPLANATION OF PLATE XXXII. 



ABBREVIATIONS. 



bl'po. Blastopore. mu. rtr. v. 



can. am. Amniotic canal. n. v. 



cav. am. ce. Amniotic cavity of the head. pr'trch. 



cav. am. so. Amniotic cavity of the trunk. ros. 



cd. d. Dorsal cord of ectoderm. sr. 



coel. Ccelom. stmd. 



crc. p'or. Postoral circlet. tab. apx. 



crc. pr'or. Preoral circlet. tab. so - 



eta. Cuticula. tab. so. d. 



en'drm. Endoderm. tab. so. v. 



gn. Supraresophageal ganglion. vt. 



ms'drm. Mesoderm. z. r. 



mu. rtr. d. Dorsal retractor muscle. 



Ventral retractor muscle. 



Ventral nerve-cord. 



Prototroch cells. 



Rosette. 



Serosa. 



Stomodseum. 



Apical plate. 



Somatic plate of ectoderm. 



Dorsal somatic plate of ectoderm. 



Ventral somatic plate of ectoderm. 



Yolk-granules. 



Zona radiata. 



PLATE XXXII. 



Figures 1 to 8 of Sipunculus nudus were copied from Hatschek ('83). Figures 10 and 15 are of Phascolosoma 

 gouldii. Figures 9, 11 to 14, and 16 are of P. vulgare. Figures 9 to 16 were drawn with the aid of an Abb6 camera 

 at a magnification of 250 diameters; Hatschek's figures were copied for a magnification of 210. 



Fig. 1. Optical sagittal section of an embryo of Sipunculus nudus, showing the beginning of the invagination of 



the endoderm plate. The cells which surround the rosette at the animal pole show a tendency to sink, 



forming the amniotic cavity of the head (Hatschek, '83, Taf. I, Fig. 8). 

 Fig. 2. Optical sagittal section of an older embryo, showing the establishment of the somatic plate of ectoderm; 



the cells of the serosa have slipped over and past the edge of the somatic plate (Hatschek, '83, Taf. II, 



Fig. 17). 



Fig. 3. Optical sagittal section, immediately before the closure of the blastopore (Hatschek, 'S3, Taf. II, Fig. 23). 

 Fig. 4. Optical sagittal section, after closure of the blastopore and formation of the stomoda-um (Hatschek, '83, 



Taf. Ill, Fig. 25). 



Fig. 5. Side view combined with optical section, showing the postoral circlet of cilia (Ilatschek, 'S3, Taf. IV, Fig. 37). 

 Fig. 6. Optical cross-section through a similar embryo, taken immediately behind the postoral circlet (Hatschek, 



'83, Taf. IV, Fig. 38). 



