MORPHOLOGY AND DEVELOPMENT OF EUDENDRIUM. 39 



There is no peculiarity in the ccenosarcal ectoderm. It is 

 columnar and has gland cells occurring singly or in groups 

 similar in type to those of the hydranth body. As we pass into 

 the larger branches it comes to consist of several layers as in 

 other hydroids. The perisarc of young branches is generally 

 homogenous. It shows lamination as it matures and often has 

 dark interior layer. 



OOGENESIS. 



Especial interest attaches to the development of the egg, be- 

 cause we have a condition hitherto undiscovered in any member 

 of the genus. It is the absorption of the neighboring cells dur- 

 ing a period of its growth. The manner in which this take place 

 does not entirely correspond with that of any other species of 

 hydroid whose oogenesis has been investigated. I confine this 

 description to the streptospadiceous gonophore as very few 

 young orthospadiceous gonophores were found. From exami- 

 nation of later stages of the latter, I am convinced that there is 

 no marked difference in their method of development. 



Origin and Migration. The interest which has formerly 

 centered in the question of the origin and migration of the eggs 

 of Coelenterata and especially Eudcndriuin has resulted in a defi- 

 nite knowledge of the facts in many of the common species. 

 Weismann, '71, and Hargitt, 'o-j 1 , have shown that the ova of 

 E. rainosuui originate in the ectoderm. Hargitt has since an- 

 nounced that in E. tonic there is a similar origin. In E. racc- 

 inosnin and E. dispar he found eggs in both layers, but the ecto- 

 derm was plainly the place of origin. 



Because there has been controversy as to the parent tissue in 

 E. rainosion, I examined several thousand sections from the 

 branches and pedicels of E. Iiargitti, that any early migration of 

 the egg from one layer to another should not escape me. With- 

 out an exception ova were found in the ectoderm. I was not 

 able to find an ovum as small as an ectoderm cell because the 

 ectoderm of the branches of mature colonies was in such poor 

 condition. The smallest ova were about three times their bulk 

 (Fig. 8). Since the eggs lie against the mesoglcea and push the 

 adjoining cells to either side by their growth, it is beyond doubt 

 that they have originated there. They occur singly. 



