MORPHOLOGY AND DEVELOPMENT OF EUDENDRIUM. 3! 



of the hydranth lies, from the first, in contact with the mesoglcea. 

 The ectoderm forms a pocket about it but does not separate it 

 on its inner side from the body wall. While it is increasing in 

 size, two entodermal processes pass out around it, the one from 

 above and the other from below ; of these the latter is the longest. 

 They meet on the outside near the top. As they approach, a 

 cup grows upward covering the surface between the lower process 

 and the stem and sending ahead on either side a short projection. 

 Growth ceases when two small spaces are left at the top, each of 

 which is nearly cut in two by one of the lateral projections. 

 . As the gonophore matures, the ectoderm secretes a perisarc 

 which remains after the contents disappear. The ectoderm, 

 itself, also becomes more opaque and tough. I find no peculi- 

 arity in the development of the egg. As one side is close to the 

 enteric cavity there is no need of a spadix tube to supply nourish- 

 ment. The entoderm of the gonophore is thrown into folds so 

 disposed that the tissue is thin in the vicinity of the egg. 



It seems probable that one type of gonophore arose from the 

 other since intermediate gonophores are sometimes found. Con- 

 ditions of occurrence and details of structure point to the strep- 

 tospadiceous as the ancestral form. It is borne on the hydranth 

 like the typical hydromedusan gonophore or medusa bud. The 

 streptospadiceous gonophore is borne on a branchlet or pedicel. It 

 grows on the younger part of the colony, is first to appear in the 

 individual colony and so may well have been the first in the history 

 of the species. The structure of gonophores and gonophore clus- 

 ters point to the same conclusion. They show further that the 

 process was one of simplification and involved a decrease in the 

 time and material used in the developing gonophore. If we 

 imagine the end of the coiled spadix to be directed upward and 

 the whole structure to flatten down on the egg, thus fusing into 

 a continuous cup whose rim is near the end of the spadix, we 

 will have a spadix of the orthospadiceous type. Further simpli- 

 fying of the gonophore by removing its pedicel and allowing it 

 to sink into the stem for a third of its diameter will make it 

 entirely orthospadiceous. Many of the large orthospadiceous 

 clusters of six or eight gonophores are divided into a proximal 

 and distal group by a small free space midway on the pedicel. 



