312 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
witli spherical bodies wbicb vary in size and stain very brilliantly. It 
is from the lower region only that gemmation of a new hydroid takes 
place, and the endoderm of the hydroid-bud consists only of these cells. 
As the bud does not develop a mouth for some little time after it is set 
free, it is possible that the spherical bodies are a store of reserve nutri- 
ment. The hydroid-bud only differs from the parent in the uniformly 
cubical shape of the ectoderm-cells, in the absence of a mouth, of nema- 
tocysts and one or two other characters. 
Ouly one specimen was available for the study of the gemmation of 
the medusoid ; in it it was formed at the apex of a polyp. The author 
gives details as to the few observations he was able to make. 
It is to be borne in mind that no free female medusoids have yet 
been found ; it is possible that there is a kind of “ male parthenogenesis ” 
comparable to the sporogony discovered by Metschnikoff' in certain 
Cuninse, when the immature sexual cells separated themselves from the 
generative organ«!, both in males and females, and began to multiply, one 
set of cells becoming engulfed by another, and, thus protected, dividing 
and redividing to form a morula, which under certain circumstances 
developed into a medusa. No conclusion can yet be certainly come to 
as to whether this remarkable form should be placed with the Trachy- 
medusm or the Leptomedusse. 
Trembley’s Experiments on Hydra.^ — Dr. C. Ischikawa has re- 
peatel and extended Trembley’s well-known experiments on turning 
Hydrse inside out. He first isolates a specimen in a watch-glass filled 
with water, fixes it firmly by its hinder end to a small glass rod, and 
then seizes the anterior end with a forked needle. The operation is 
very easy, and after a little practice, one can invert a Hydra in five or six 
minutes. Care must be taken that there are no Daphnid-tails in the 
stomach, as their sharp edges easily destroy the endodermal cells. To 
try and prevent the creatures returning to their original relation of 
parts, a bristle was passed through them. 
The inverted Hydrse will regain their original position if it is in 
any way possible to them, and if they cannot they die ; the bristle does 
not stoj) their activity. The return to the original position is often so 
rapid that it may be easily overlooked unless the creatures are con- 
tinuously watched. If part of a body of a Hydra be cut off, the new 
head is always developed at the anterior end ; this fact is not in accord- 
ance with Nussbaum’s view that the ectodermal cells of an inverted 
Hydra creep over and cover the endoderm. The intermediate cells are 
not able to regenerate all the lost cells of the body ; they are young 
ectodermal cells, and as such can only replace the lost ectodermal cells. 
A small piece of ectoderm completely freed from endoderm is never 
regenerated into a complete animal ; at the same time the intermediate 
cells of such a piece live and multiply for some time after the operation 
by budding. 
If a Hydra attempts to take food which is so large as to extend the 
mouth too much it turns itself inside out around it, and immediately 
returns to its original position ; this fact is of interest as explaining the 
2)ossibility of an artificially inverted Hydra returning to its original 
* Zeilschr. f. Wiss. Zool., xlix. (1889) [1890] jip. 433-60 (3 pis.). 
