1910] Robertson: Cyclostomatous Bryozoa. 227 



fertile zocecium which gives rise to the ovum from which the 

 embryos are developed. Unlike the Chilostomata, few of the 

 zocecia of the Cyclostomata produce ova, and the number of 

 ovicells of a given colony correspond to the number of fertile 

 zocecia. While relatively few ovicells may be produced, the 

 number of larvae to which a colony may give rise, however, is by 

 no means small. This is due to the interesting process of poly- 

 embryony which occurs quite generally throughout this sub- 

 order. As has been shown by the present writer ( :03), not only 

 are relatively few ova produced, but of these still fewer come 

 to maturity. Each ovum which matures does so in an ovicell or 

 ooecium, in which it develops into an embryo of relatively enor- 

 mous size. The outline of such an embryo not yet of full size 

 is shown mi pi. 18, fig. 4, emb. This, instead of forming a single 

 larva, proceeds to bud, or fragment, each bud, or secondary, or 

 ■even tertiary embryo giving rise to a larva. Thus, each egg 

 produces a large number of embryos, as many as 150, or more. 

 These secondary embryos remain within the sheltering walls of 

 the ovicell until they acquire cilia and are able to live a free 

 existence, when they are set free, each one capable of producing a 

 new colony. In the large ooecium of Lichenopora, the large 

 embryo may often be found sending its arms, or branches, into the 

 vacant spaces between the rows of zocecia. The larvae escape 

 from the ooecium by an openihg which has been found to be 

 characteristic and to be useful in diagnosis. For this ocecial 

 aperture Harmer has devised a terminology which has been 

 adopted throughout the descriptions of species in this paper. 

 The opening from the ooecium, i.e., the passage by which the 

 larvae escaped from the ovicell, is the oceciostome. This may or 

 may not possess a tube or funnel. If a tube is present through 

 which the larvae must pass before reaching the outside this is 

 simply known as the tube of the ooeeiostome. Its external opening 

 is known as the oceciopore. Sometimes the tube is absent and 

 ooeciopore and oceciostome coincide. The tube of the ooeeiostome 

 frequently resembles a zooecium in shape and size, and in the 

 case of large ovicells which include numerous zon?cia it may be 

 almost indistinguishable from a zooecium. It may usually lie 

 detected, however, by the size and number of the pores piercing 

 its wall. The tube of the ooeeiostome beins' a direct continuation 



