ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
801 
The processes observed in Bougainvillea and Tubularia cannot be 
adapted to the schemes of Hydromedusan development which have been 
sketched by Metschnikoff and Tichomiroff. In both these forms there 
is a process of migration, as well as delamination. The modes of 
germinal layer formation seen in Bougainvillea and Tubularia are 
distinguished from those described by Metschnikoff for the Craspedota 
in that the result of migration is not a planula with sharply limited 
layers, but a compact stage with completely identical cells. This 
stage may be called that of the pseudomorula. 
This formation of a pseudomorula by means of migration instead 
of a planula, may be partly explained by supposing that the coelo- 
blastulae do not represent free living forms, as in the Craspedota. A 
stage of specialization in which the migrating cells can be easily 
distinguished from those of the blastoderm has not yet been reached. 
The specialization of the ectoderm-cells and the formation of the 
structureless lamella is here not an act of germinal-layer-formation, 
but the further development of the peripheral layer of the pseudo- 
morula. 
Budding in Hydra and some Hydroid Polyps.* — Herr A. Lang has 
examined the mode of budding in Eudendrium ramosum, E. racemosum , 
Plumularia echinulata , and Hydra grisea. He finds in all four that the 
bud does not, as has been hitherto believed, form an evagination of the 
common body-wall at a definite point, but that it is formed by the ecto- 
derm only of the parent. What happens is this ; the ectoderm thickens 
in a zone of gemmation which is definitely fixed for each species ; it is 
due to a steady division of the cells of the ectoderm ; in Hydra and 
Eudendrium the division occurs in the so-called indifferent or interstitial 
cells ; and the division is ordinarily transverse, and is always indirect. 
The growth of the ectoderm goes on for some time without any changes in 
the endoderm of the area of gemmation. When the thickening is of some 
size, the cells that lie next the supporting lamella break free and begin 
to wander through it. The cells which lie on the endodermal side of the 
supporting lamella and their successors form the endoderm of the bud. 
Between them and the still growing ectoderm the supporting lamella is 
formed anew. In Hydra and E. ramosum there may be seen, in sections, 
numerous cells whose protoplasmic processes clearly point to their 
power of independent amoeboid movement. 
The endoderm of the coenosarc at the point of budding is pushed out 
by the young bud-endoderm, and is gradually absorbed partly by it and 
partly by the neighbouring endodermal cells of the coenosarcal tube. 
The young bud-cells quickly grow to the size of typical endodermal 
cells. It may easily be seen in Hydra that it is only definite cells of 
the thickened ectoderm that are converted into endodermal cells, while 
others become stinging or epithelio-muscular cells. 
The gastric cavity of the primitively solid bilaminate bud arises 
from a cleft which is formed internally to the altered ectodermal cells. 
If we compare the gemmation of Hydroid Polyps with their em- 
bryonic development we find striking points of resemblance. If we 
compare the ectoderm of the area of gemmation to the blastoderm, the 
* Zeitschr. f. Wiss. Zool., xlv. (1892) pp. 365-85 (1 pi.). 
