REPORT ON THE PENNATULIDA. 265 



EEPORT ON THE PENNATULIDA 



COLLECTED IN THE OBAN DKEDGING EXCURSION 



OF THE BIRMINGHAM NATURAL HISTORY AND 



MICROSCOPICAL SOCIETY, JULY, 1881. 



BY A. MILNES MARSHALL, M.A., D.SC, PROFESSOR OF ZOOLOIJV 

 IX OWENS COLLEGE, AND W. P. MARSHALL, M.I.C.K. 



t Concluded from page 250. ) 



(J. The Reproductive Organs. — The eggs in Virgularia occupy a very- 

 different position to that they hold in FunicuUna ov Pennatula. They 

 are confined to the lower part of the rachis, and only occur in that 

 part of it in which the polypes are either absent or very immature. 

 In this lower part of the rachis, a transverse section across which is 

 represented in Fig. 6, the canal system of the mesoderm becomes very 

 greatly developed. In addition to the four main canals ((/) there are 

 large lateral chambers Imed by endoderm, and from this endoderm at 

 certain places the ova {t) are formed, and when ripe fall into the 

 chambers, in which they lie free. 



The actual development of the ova themselves is much the same as 

 in the other two genera. Each ovum is a single endoderm cell which 

 becomes bigger at the expense of its neighbours, rises up from the 

 surface to which it remains attached by a stalk or peduncle, developes 

 a firm protective capsule round itself, acquires a large germinal vesicle 

 with included germinal spot — the nucleus and nucleolus respectively 

 of the original eudodermal cell^and having attained its full size 

 becomes detached from the stalk and lies free in the chamber of the 

 rachis. How the eggs get out ultimately we have been unable to 

 determine with certainty ; most probably their exit is effected through 

 the mouths of the polypes higher up the rachis, whose body-cavities are 

 in connection with the large chambers of the lower or ovarian end of 

 the rachis. 



The essential difference between Virgularia on the one hand, and 

 FunicuUna and Pennatula on the other, so far as their reproductive 

 organs are concerned, lies in the fact that while in the latter two 

 genera the reproductive elements, ova or spermatospheres, are developed 

 within the polypes, in Virgularia they are formed independently of the 

 polypes, and in a part of the rachis where the polypes are either 

 altogether absent or at least very immature. 



It will be remembered that in FunicuUna we described and figured 

 the occurrence of ova in the canal system of the rachis (Plate II., Fig. 

 10, t), and left it uncertain how these ova got into canals which, 

 except at the points where they lie, are much too small to admit them. 

 The condition of things in Virgularia renders it not improbable that 

 these ova have originated and been developed in the position in 

 which we find them within the canals. 



