Poe HN DX. 
ADDENDA AND ANNOTATIONS. 
Reproduction in the Hydroidea,—p. 22. 
. 
Tue observations of Van Beneden, on the Tubularide, but lately published, have 
brought out many new facts with regard to the structure and modes of reproduction cha- 
racterizing this division of the Hydroidea.* His investigations have led him to distin- 
guish the following modes of reproduction : 
1. By persistent buds, by which, as in the Sertulariz, and in zoophytes generally, 
compound groups are formed. < 
2. By caducous ovule-like buds or gemmules. These are produced about the bases of 
the tentacles, and have been considered true ova (pp. 22, 23), to which they are clasely 
analogous. Van Beneden describes them as presenting within, when complete, a distinct 
cellule, which he considers as corresponding to the germinant vesicle of the true egg. 
This cellule enlarges, and shortly a membrane forms across, which is in contact below 
with the circulating fluids of the axis; from this membrane the new polyp proceeds. He 
traces out the changes in progress from this state to the developement of the medusa-like 
young, a Beroe in form,—a floating pellucid disk, fringed around with delicate tentacles, 
and furnished with eight eyes. 
3. By a single ovule, thus approaching in character the Actinoidea. 
Besides the above modes, he mentions also two others, 
4. Compound ova, resulting in each instance from a production of numerous ovules 
from the yolk of what at first appears to be a simple ovum, each ovule having its own 
germinal vesicle, and producing separate young. 
5. Ovules formed within the caducous gemmules. This mode corresponds nearly to 
known instances of ova in larvee or undeveloped young. ‘These develope and take the 
form of a Planaria, and are the Planules of Sir J. G. Dalyell. (Fourth Rep. Brit. Assoc., 
1834, p. 602.) From the Planule, a kind of larve, the perfect animal afterwards proceeds, 
* Van Beneden’s very elaborate Memoir is just published in the Transactions of the Royal Society of 
Brussels. A short abstract of it is given in a late number of L’Institut, and also in the Annals and 
Magazine of Natural History, vol. xv., p. 346 ; and these are the only sources of information with regard 
to it which the author has had. 
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