A NK\V FAMILY OF HYDKOIUKA. 



bounded by dark lines, indicating the edges of the perisarc, and is studded with 

 nematophoree seen at the edges of the branch. Hy. Hydrothecae. P. nematophores. 



Figure 7. A longitudinal section of a small branch, showing the skeleton. The 

 tubes of which the branch is composed are seen to be very irregular, but to run, 

 r>i>irially towards the central part, in a direction generally parallel to the length of 

 the branch. E. spaces or grooves, immediately beneath the thin external layer. 

 Hy. hydrothecae. P. thin external layer of perisarc. P'. the continuation of P. 

 to form an operculuin at the mouth of the hydrothecae. P". the iieinatophores. 

 x35. 



Figure 8. A transverse section of a small branch, to show the tubes of which it 

 is composed. The tubes vary in size, and open into one another. The outer ones 

 are incomplete externally, forming grooves, the lips of which are usually touched by 

 the thin external layer of perisarc. Two hydrothecae are cut through. The perisarc 

 is thicker towards the outer than in the inner part of the branch. Letters as in 

 Fig. 7, x 70. 



Figure 9. A small portion of the external part of a branch very much enlarged 

 to show the roughly concentric layers of which the perisarc is formed. Letters 

 as in Fig. 7. 



Figure 10. Small portion of a ccenosarcal tube with the perisarc walls from 

 the interior of a branch. Ect. the ectoderm in which the outline of the cells cannot 

 be clearly distinguished, and which varies in thickness in various parts coming in 

 contact, in certain places, with the perisarc walls. End. the unilaminar endoderni, 

 the cells of which are larger than those of the ectoderm, x. globular structures of 

 unknown significance containing darkly staining parts which lie apparently within 

 the cavity of the tube. Drawn under Zeiss F. oc. 2. 



Plates 21, 22, 23 refer to Plumularia procumbens. 



PLATE 21. 



Figure 17. Restoration of the soft parts only of Plumularia procumbens. The 

 polysiphonic stem is shown in section with the transverse connections between the 

 various tubes which compose it. Down the centre runs the main tube from which 

 arise all the lateral branches pinnae and hydrocladia which are in connection with 

 a varying number of the surrounding tubes. The most external ones give off 

 numerous machopolypes, and on the pinnae are shown the groups of polypes, each 

 consisting of one gastrozooid and three machopolypes. One blastostyle is shown 

 with a gonophore, arising from the angle between a pinnule and the main stem of the 

 pinna, x 30. 



Figure 18. Longitudinal section of a male gonangium with its contained 

 blastostyle and gonophore. In the centre of the gonophore lies the mauubrium. Bl. 



