MARINE POLYZOA. 5 



number of holes, or rather is wanting in a certain number of spaces, 

 for which spaces the term " fenestrae " is here employed. These 

 apparent openings, therefore, do not penetrate into the cavity of 

 the cell. But besides the fenestrae, there is in some cases a small 

 central opening which does penetrate through the wall. In most 

 cases the fenestrae are arranged in a crescentic, or rather horse- 

 shoe-shaped line, indicative as it were of the limits of a regular 

 oval space in the front wall of the cell, the upper part of which 

 oval would be formed by the mouth, and the remainder filled up 

 by the deposition of calcareous matter, as happens in the older 

 cells of many other of the Cheilostumata. 



A further characteristic of the fenestrate Catenicellce is the ter- 

 minal position of the ovicells. These organs are clearly trans- 

 formed cells, or cells dilated to considerably more than their natu- 

 ral bulk, and assuming a subglobose form ; and, what is worthy 

 of remark, these terminal ovicells always have a sessile avicula- 

 rium on the summit. 



In the "Vittatae" the cell is smaller, and usually more delicate 

 and transparent. They probably want the outer lamina, or have 

 it very thin, and consequently present no fenestrate spaces, and 

 the front of the cell is beset (sometimes very sparingly) with more 

 or less prominent, minute, acuminate " papilla?." On each side, 

 sometimes on the anterior aspect, sometimes quite laterally, is a 

 narrow elongated band, or " vitta " as it is here designated, from 

 which the sectional appellation is derived. This band or stripe 

 (the nature of which is unknown) varies in width and propor- 

 tionate length and position in different species ; it is slightly ele- 

 vated, and marked with larger or smaller circular, discoid, or acu- 

 minated eminences. This subdivision is further distinguished by 

 the situation of the ovicells, which are not terminal, but occur at 

 irregular intervals on cells in the course of the series. They are 

 of the ordinary galeate form, but are not apparently placed above 

 the mouth 'of a cell, as is most usual in the Cheilostomata, but 

 below it in front. In all cases the shape of the ovicelligerous cell 

 is very different from the rest, and in all the vittate species it 

 arises from its predecessor, without the intervention of a short 

 tube, but is immediately sessile upon it by a broad base. This 

 conformation is well seen in C. gibbosa (PL VII. figs. 3, 4). It is 

 not improbable, however, that the inferior position of the ovicell 

 is more apparent than real, and that in fact the ovicell, which ap- 

 pears to be inferior in the upper of the two cells, really belongs 

 to the one below, and is merely, as it were, immersed in the base 

 of the upper one. In one instance, C. taurina (PI. XI. fig. 3), the 

 situation of the ovicell is peculiar : in this species the ovicelli- 

 gerous cell is geminate, the ovicell being placed on the summit of 

 a secondary cell, on the side of the one forming part of the series. 



