EMBRYONIC FISSION IN CYCLOSTOMATOUS POLYZOA. 19 



Next to the ectocyst comes a very definite nucleated layer, 

 which encloses a network of cells separated by smallish 

 vacuoles. 



In later stages the outer definite layer of nuclei disappears, 

 and the network becomes continuous with the reticulum 

 formed by the modification of the follicle (fig. 11). The basal 

 network of cells is obviously part of the ordinary funicular 

 tissue, which, as has already been pointed out, forms a con- 

 tinuous connection from zooecium to zooeciura, or from zorecium 

 to ovicell, through the pores in the calcareous septa between 

 neighbouring individuals. It can hardly be doubted that the 

 rich protoplasmic reticulum iu which the young larvae lie is 

 the means by which nutriment is conveyed to the developing 

 larvae. 



Fig. 10 is a stage of which I obtained only one example, 

 and I cannot be sure that what is there represented is really a 

 normal process. This preparation indicates that a kind of 

 invagination takes places in the embryo at this stage (which is 

 certainly very near that shown in fig. 9). If this is really 

 correct, the inner layer of the primary embryo may possibly 

 be formed by a process of invagination, and the inner layer of 

 the secondary embryos is then probably derived from this 

 invaginated layer; but I make these suggestions with all 

 reserve. 



Fig. 8 is interesting partly because it supports the view 

 advanced in my former paper (17) that the species there 

 described as C. ramosa is not identical with C. eburnea. 

 The figure is a longitudinal section of an ovicell of C. 

 eburnea; and so far as the general development of the ovicell 

 goes, the age corresponds with the stage shown, for C. 

 ramosa, in fig. 6. 



The tentacle-sheath is at its period of maximum develop- 

 ment ; but the relative sizes of follicle and embryo are widely 

 diff'erent from their relative sizes in C. ramosa. This 

 appears to be a constant difi'erence between the two species. 

 In C. eburnea, the follicle is reduced to a minimum, and the 

 quantity of the protoplasmic reticulum of mature ovicells is. 



