140 A NEW FAMILY OF HYDROIDEA. 



blastostyle, D. swollen distal, end of blastostyle. Sp. si3erm. G. walls of 

 gonotheca. 



Figure 19. — Transverse section of a male gonangium and gouopliore. On the 

 left side between the gonophore and the wall are seen traces of the much compressed 

 blastostyle. End. endoderm of manubrium. Ect. ectoderm outside sperm cells {sp.) 



Plate 22. 



Figure 20. — Portion of a colony of Plumiilaria prociimbens showing the poly- 

 siphonic stem and the pinnae arising irregularly from this, x 1\. 



Figure 21. — Much enlarged portion of a pinnule or hydrocladium to show the 

 alternate longer and shorter joints. The latter bears no hydrotheca or 

 nematophores ; the former bears a hydrotheca with the nematophores at 

 the level of the mouth of the former, and one in the median line 

 below. The thickenings in the walls of the pinnule are shown in their positions 

 and the two nematophores in the axil between the pinnule and the main stem of the 

 pinna, and at A, the conical structure opening to the exterior. N^. upper pair of 

 nematophores. N^. lower median nematophores. N^. nematophores in the axil of 

 the pinnule and pinna stem. A. conical process in the axil leading from the interior 

 of the pinna to the exterior. 



Figure 22. — Much enlarged view of a nematophore seen in optical section, and 

 showing the two chambers. 



Figure 23. — Much enlarged view of a male gonangium. 



Figure 24. — Semi-diagrammatic drawing of a longitudinal section of the poly- 

 siphonic stem of the same to show the relationship of the hard and soft parts and the 

 distinctness of the central tube with its walls slightly yellower than those of the 

 surrounding tubes. C. central tube. H. central stem of pinna. H'. hydrocladia. 

 L. lateral tubes. N. nematophores. T. transverse connections uniting the various 

 tubes, x 30. 



Plate 23. 



Figure 25. — Much enlarged view of the termination of a polysiphonic stem, 

 showing the numerous nematophores on the stem and the pinn* &c., arising 

 irregularly. The basal parts of the pinnfe are strengthened by the formation of a 

 thick perisarc wall continuous with that of the tubes forming the stem, x 20. 



Figure 26. — A highly magnified portion of a pinna. 



Figures 27 and 28. — Transverse sections of the polysiphonic stem to show the 

 component tubes — skeleton only^ — with the large central one, from which in figure 28 

 a pinna is arising. The external tubes are studded with nematophores. 



