ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
489 
intermediate ectodermal layer, and these increase in size till they come 
to lie next the supporting lamella. The cells of the endodermal evagi- 
nations undergo marked changes, lose their connection with the rest of 
the endoderm, and lie in the middle mass in the form of closed cylindri- 
cal tubes. The outer ectoderm layer now sends inpushings between the 
tubes, and eventually grows completely around them. 
The rudiment of the bud thus formed consists of an endodermal 
tube which lies in the middle mass of cells, surrounded by a supporting 
lamella and overlaid by ectoderm. The buds, which are formed from 
both ectoderm and endoderm, are found as evaginations, in the usual 
mode of budding in Ccelentera. After the bud begins to form the 
reproductive organ generally enlarges to several times its usual size ; 
the radial canals enlarge, and quantities of food may pass into the cavity 
of the reproductive organ for digestion. 
Polydonia frondosa.* — Mr. E. P. Bigelow has made some observa- 
vations on this Medusa, the most interesting of which refer to its sexual 
dimorphism, the female presenting a special adaptation for the protec- 
tion of the eggs. In immature forms of both sexes aud in males, the 
appendages of the oral disc have the same structural arrangement as 
those of the oral arms. In the adult female the oral funnels disappear 
from the disc, while the oral vesicles increase in number till they com- 
pletely cover it. The eggs are discharged from the ovaries into the 
stomach, where cleavage commences ; they then pass out on to the oral 
disc, where they are cemented in small reticulated clusters at the bases 
of the vesicles; and they remain there till they become free ciliated 
planulse. 
The vesicles on the arms have the function of capturing food. If a 
vesicle be rubbed gently with a glass rod, there is an immediate con- 
traction of the muscles on the side stimulated, so that the vesicle, which 
usually stands upright, is suddenly bent down, and closes the mouth of 
the nearest funnel. A copopod | striking one of these vesicles is im- 
mediately stung by the nettle-cells, and, before it can escape from them, 
it finds itself within an oral funnel, tightly shut in by the overlying 
vesicle. 
The slime that surrounds the disc may serve also to entrap micro- 
scopic food, but, from the experiments which the author has made, he 
concludes that the usual food of these jelly-fish is not, as is often 
supposed, microscopic material, but copopods captured in the way 
described. 
Development of Stinging Organs in Hydroids.J — Herr L. Murbach, 
in a preliminary notice, states that he finds that the fission of the so- 
called interstitial cells, which leads to the formation of the stinging 
cells, is always amitotic. In the cell that forms the stinging capsule 
part of the nuclear mass is localized at the periphery of the nucleus 
to form a highly refractive, often curved, rodlet which is especially 
remarkable for its power of taking stains. The presence of a rodlet of 
this kind is characteristic of the developing stinging cell. The rodlet 
soon migrates from the nucleus into the cell-body, where it forms around 
* John Hopkins Univ. Circ., xii. (1893) p. 106. 
f So spelt, apparently correctly, by Mr. Higelow. 
% Zool. Anzeig., xii. (1893) pp. 174 and 5. 
