211 



tained a certain size their presence is already shown on regarding the frontal 

 surface of the respective zocecia, the lattei- then being half transparent. Pis. VII 

 and VIII show difierent stages in development of such ooecia in Cell, australis. 

 Cell, rigida and Cell atlantica. 



The avicularia, only occurring in small numbers, vary much both in size 

 and form, and the largest of them, the dimensions of which are similar to those 

 of the zocecia, reach right to the axis of the colony, while this is not the case 

 with the smaller of them, the latter being only wedged in between the zocecia. 

 Judging from the figures given by Busk in his account of the Bryozoa of the 

 Challenger Expedition we should imagine that these avicularia had constantly a 

 complete subopercular cryptocyst. But although the latter may be unusually 

 strongly developed, it is only in exceptional cases and in older zocecia, e. g. in 

 Cell, fistulosa, that it reaches right up to the operculum. As a rule it has either 

 one median or two symmetrical incisions distally, and in Cell, malvinensis, which 

 is in fact one of the species figured by Busk, the median incision is separated 

 from the opercular area by a tiny cryptocyst arch, which unites the two inner 

 ends of the suspensory facets of the mandible. 



The very peculiar fact, that the areas perceptible on the surface of the colony 

 are by no means equal in size and extent to the zocecia, has hitherto escaped 

 notice, and Busk's description of the separate superficial divisions as » areas « is 

 in accordance with his incorrect conception of the above mentioned filiform chi- 

 tinous thickenings as a system of hollow filaments shared in common by the 

 whole colony, imbedded in and effecting the growth and the calcification of the 

 separating walls, which he imagines to exist between the separate areas. There 

 can however be no doubt that Busk thinks every area to correspond with a 

 zooecium (»Zooecia completely immersed, each corresponding to an area« ^). That 

 the areas and the zocecia do not correspond in this family is most easilj^ seen 

 on isolating a single zooecial layer of Cell, atlantica and grinding away the basal 

 wall (fig. 2 c), as the narrow elongated zocecia and the much shorter and broader 

 rhombic areas may then be seen at the same time. In regarding a longitudinal 

 grinding it will also be very obvious that the ocecia, the bottom of which is a 

 part of the separating wall between two zocecia lying in the same longitudinal 

 I'ow, open in the distal part of an area but in the proximal part of a zooecium 

 (PI. VIII, figs, la, lb. PI. VII, fig. 4 f). 



We may now by means of longitudinal and transverse sections make a closer 

 inspection of the way in which the separate zocecia are mutually connected in 



'8, p. 83. 



14* 



