80 SIDNEY F. HARMER. 



they certainly do in Lichenopora. In transparent prepara- 

 tions it can be seen that the cavities of the two lobes remain 

 separated by a vertical radial septum, the upper edge of which 

 is generally indicated as a line on the roof of the ovicell even 

 in dried colonies (fig. 5.s.). 



As the radial series of zooecia are formed all round the peri- 

 phery, the ovicell itself consists of a cavity which branches 

 dichotomously at the proximal end of each series. In large, 

 actively growing colonies (fig. 5) the ovicell usually branches 

 in a palmate manner, and the primary lobes may undergo 

 further dichotomy once or more. The extent to which the 

 ovicell branches is not a specific character, but is probably 

 dependent partly on nutrition and partly on temperature. 

 Figs. 2 and 4 represent mature fertile colonies of T. aperta 

 and T. flabellaris respectively, and fig. I a fertile lobe of T. 

 pluraosa. The ovicell shown in the last figure is much 

 more complicated than that shown in the former two; but it 

 must be distinctly understood that the ovicell of T. flabel- 

 laris and T. aperta may be large and much branched in 

 vigorous colonies. 



After the ovicell has reached a certain size it develops its 

 tubular portion, ending in the orifice through which the larvae 

 make their escape. Here, however, there is some modification 

 in the course of the development as compared with an ordinary 

 zooecium. While the orifice of the latter is merely the part 

 which, for the time being, forms the distal end of the zooecium^ 

 the lobes of the ovicell undergo a considerable amount of 

 growth, in most cases, after the orifice is fully formed. Sooner 

 or later, however, the peripheral ends of the lobes, closed 

 merely by a soft terminal membrane during growth, become 

 completely calcified, except in the abnormal specimens of T. 

 aperta (fig. 2), described under the heading of that species, 

 in which accessory openings may be formed by the outgrowth 

 of the lobes into tubular passages which more or less resemble 

 the real orific^ of the ovicell. The complete calcification of 

 the peripheral eno^f the lobes of the ovicell takes place, as 

 in other Cyclostomes, by the encroachment of the calcareous 



