ON THE DEVKLOPAJENT OP TUBULIPORA. 127 



between the two genera may be due to the fact that in 

 Lichenopora the ovicell dominates the entire colony, whereas 

 in Tubulipora new fertile lobes can be developed in colonies 

 which possess an old ovicell (fig. 1). It must further be noted 

 that the specimens of Tubulipora were collected early in the 

 year, and therefore early in the breeding season. 



Stage B. — Division of the Egg, and Degeneration of the Fertile 



Polypide. 



The number of polypides which become actually fertile is a 

 strictly limited one, as in Lichenopora. The bilobed con- 

 dition so often characteristic of the young colony is usually 

 correlated with the development of two ovicells. These are at 

 first ordinary zooecia, as in Lichenopora; and in T. flabel- 

 laris and T. aperta the proximal end of the ovicell not un- 

 commonly has the external characters of a zooecium, the 

 increased number of pores which denote the ovicell beginning 

 in some cases suddenly when the zooecium has reached a 

 certain length. But in all species it is easy to see, by looking 

 down into the young ovicell at a time when it is commencing 

 to expand, that the dilated part of the ovicell is continuous 

 with a prismatic or pyramidal cavity which runs proximally 

 into the general series of zooecia. A convenient way to demon- 

 strate the fact that the proximal end of the ovicell is morpho- 

 logically a zooecium is to stain a colony which possesses a 

 young ovicell without decalcifying, and to embed it in paraffin. 

 By scraping away the lower or basal wall of the colony, and 

 then dissolving out the paraffin and mounting whole, a view of 

 the lower surface can be obtained without having the details 

 obscured by the relatively thick, calcareous, basal lamina. 

 In preparations of ovicells of a suitable age made in this way 

 (fig. 30) the young embryophore may be demonstrated in a 

 part of the ovicell whose floor is the basal lamina, and in fact 

 in a cavity which in no way differs from an ordinary zooecium. 



The fertile zooecia of Lichenopora are usually difl'erentiated 

 at an extremely early stage in the life of the colony. In 



