284 



DR J. H. ASHWORTH AND DR JAMES RITCHIE ON THE 



Delage, Y., et Herouard, E., 1901, " Les Ccelenteres," in Traite de Zoologie concrete, t. ii, pt. 2. 



Gerd, W., 1892, " Zur Frage uber die Keimbliitterbiklutig bei deii Hydromedusen," Zool. Am., vol. xv, 



pp. 312-316. 

 Goette, A., 1907, " Vergleichende Entwicklungsgeschichte der Geschlechtsindividuen der Hydropolypen," 



Zeitschr. wiss. Zool., Bd. lxxxvii, pp. 1-335. 

 Harm, K., 1902, "Die Entwicklungsgeschichte von Clava squamata," Zeitschr. wiss. Zool., Bd. lxxiii, 



pp. 115-166. 

 Hartlaub, O, 1897, " Die Hydromedusen Helgolands," Wiss. Meeresunters. deutsch. Meere, pp. 449-536. 

 Hincks, T., 1868 [1869], A History of the British Hydroid Zoophytes, London, 2 vols, 

 Kemna, A., 1908, " Morphologie des Ccelenteres," Ann. Soc. roy. Zool. Malacol. Behjique, t. xliii, 



pp. 229-337. 

 Kuhn, A., 1910, "Die Entwicklung der Geschlechtsindividuen der Hydromedusen," Zool. Jahrb., Anat. 



u. Ontog., Bd. xxx, pp. 43-174. 

 Weismann, A., 1883, Die Entstehung der Sexualzellen bei den Hydromedusen, Jena. 



DESCRIPTION OF FIGURES. 



List op Reference Letters. 



B i, B ii, B in, B iv, B v, blastostyles. 

 C, cuticle. 

 CO, covering cell. 

 Cosl., ccelenteron. 



D., debris adherent to perisarc. 

 Ect., ectoderm. 

 End., endoderm. 

 Ex.C, excretory cell. 



H i, youngest hydranth of colony. 

 M., mesogloea. 

 N., nematocyst. 



P., partition formed across lumen of stolon. 



Pe., perisarc. 

 P.Z., peripheral zone of oocyte containing fine 



granules. 

 S.N., sporosac-neck. 



Sp., spermatogonia. 

 Spd., spadix. 

 Spz., spermatozoa. 

 S.S., sporosac-stalk. 



St., stolon. 



T., tentacle. 



Plate VI. 



Dicuryne conybearei (Allman), from Naples. 



Fig. 1. A portion of a colony showing a recently formed hydranth (Hi) with six tentacles, and three 

 larger hydranths, one bearing a blastostyle-bud (Bv) in the ectoderm of which several oocytes are seen. 

 Arising from the stolon are three young blastostyles (Bi, En, Bin) and one full grown (Biv), the latter 

 bearing twenty-two sporosacs, fifteen of which are seen. It is exceptional for a blastostyle so small as B n 

 to exhibit such large oocytes and elevations of the ectoderm (i.e. incipient sporosacs). Two free female 

 sporosacs (S i, S n) and one free male (S in) are also shown ; the male was produced on another colony. The 

 stolon was covered with debris (omitted, except in a small area on the left), and there was also a considerable 

 amount of debris on the perisarc, Bhown only on the large central hydrocaulus. x 75. 



Plate VII. 

 All the figures relate to Dicoryne conybearei (Allman), from Naples. 



Fig. 2. Longitudinal section through the wall of a blastostyle, showing a large oocyte in the ectoderm. 

 The space around the oocyte is an artefact. For further description see p. 263. x 1000. 



Fig. 3. Longitudinal section of a young sporosac and the adjacent wall of the blastostyle which bears it. 

 See p. 263. x 1000. 



