FREE-SWIMMING SPOROSACS OF THE HYDROID GENUS DICORYNE. 285 



Fig. 4. Longitudinal section of an older and almost full-grown sporosac. For description see p. 263. 

 x 1000 



Fig. 5. Free-swimming, ciliated female sporosac. See p. 264. x 500. 



Fig. 6. Female sporosac after escape of the egg by rupture of the ectoderm. x 500. 



Fig. 7. Section of a portion of the ectoderm at the distal end of a blastostyle, showing a discharged 

 nematocyst of the large, elongate oval type. See p. 262. x 1400. 



Plate VIII. 

 All the figures except fig. 16 relate to Dicoryne coinjhearei (Allman), from Naples. 



Fig. 8. Longitudinal section of the ectoderm and mesoglcea of a male blastostyle, showing the first 

 differentiation of the male sexual cells. In addition to the two spermatogonia represented there was a third 

 lying immediately underneath them (i.e. at a deeper level). See p. 265. x 1000. 



Fig. 9. Longitudinal section of the wall of a male blastostyle showing two stages in the formation of 

 sporosacs. On the left of the figure note the spermatogonia in the ectoderm ; the mesoglcea is already bend- 

 ing outwards. In the later stage shown on the right of the figure numerous spermatogonia are seen in 

 the ectoderm at the distal end of the sporosac, and peripheral to them are, here and there, cells with paler 

 protoplasm and smaller nuclei which will later form the covering cells. There is a small central cavity in 

 the endodermal spadix, but it is filled with granular matter. See p. 265. x 1000. 



Fig. 10. Longitudinal section of a free-swimming male sporosac. See p. 266. x 500. 



Fig. 11. Section of a blastula consisting of about 120 to 130 cells. See p. 277. x 500. 



Fig. 12. Section of a later stage of development; the cleavage cavity is now filled with a mass of 

 endoderm cells. See p. 278. x 500. 



Fig. 13. Section of a still later stage in which the ccelenteron has been formed by breaking down of 

 some of the endoderm cells, the debris of which lies in the cavity. See p. 278. x 500. 



Fig. 14. Horizontal section of a portion of the stolon, showing the thick perisarc, the adherent debris, 

 and the internal partitions (P i-P iv) formed successively by the coenosarc as it retreated under the influence 

 of deleterious conditions. See p. 260. x 250. 



Fig. 15. Horizontal section of another portion of the stolon, showing the coenosarc, here composed of 

 ectoderm with a solid mass of endoderm, secreting a chitinous barrier across the lumen of the stolon. The 

 coenosarc has contracted away from the perisarc. x 500. 



Fig. 16. Dicoryne conferta (Alder). Median section, in the plane of the tentacles, of a mature male 

 sporosac ready to be released from its stalk. In most spadices of this species there is at maturity a central 

 cavity. Note the great thickness of the mesoglcea in the wall of the blastostyle. Compare with figs. 4 

 and 10. For further description see p. 267. x 500. 



PRES 



TRANS. ROY SOC. EDIN., VOL. LI, PART 1 (NO. 6) 41 



