ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
165 
some reason lost the power of secreting a skeleton, must for the present 
be left an open question. 
Some Ectosarcal Phenomena in the Eggs of Hydra.* — Prof. E. A. 
Andrews finds that, in addition to the various granular pseudopodia that 
accompany the remarkable cleavages of the eggs of Hydra , there are 
peculiar disturbances of the ectosarc; clear films and filaments being 
freely formed. These outgrowths of the ectosarc are formed when and 
where the parts of the egg are separated by considerable space, and ex- 
tend out into such spaces. They undergo great changes of form and of 
bulk, and may suddenly emerge, withdraw, bend, or branch. At the 
bottom of cleavage furrows, when closing, such ectosarcal processes may 
reach across the cleft to the opposite cell or mass, and they may be con- 
cerned in the approximation and union of cleavage products. The 
phenomena are akin to those which the author calls “ filose,” and there 
is good reason to suppose them produced by such changes in the ectosarc 
as can at present be spoken of only as contractility. By contractions 
also in the material of the processes themselves, some, if not all, of their 
changes of form and size seem to be brought about. 
Porifera. 
Observations on Sponges.f — Messrs. G. C. J. Vosmaer and C. A. 
Pekelharing give an account of their observations on sponges. First of 
all, they deal with the nutrition, and state the results of feeding Spon- 
gilla lacustris and Sycon ciliatum with carmine and with milk. They 
believe that they are entitled to say that the choanocytes really are the 
organs by which particles suspended in the water, passing through the 
canals, are captured, and thus brought into the tissue of the body. A 
number of facts are cited which suggest that there is a whirling move- 
ment of the water in the flagellate chambers, and not a regular water 
current passing quickly through. The authors go on to show that the 
irregular motion of the flagella is not inconsistent with the regular 
current through the canals. Their explanation will hold good only if 
the current is in one direction, and the authors are unable to accept the 
observation that the current may be sometimes reversed. 
In closing their discussion of the currents, the authors say, “We 
have in sponges an example of the height and fitness of organisation 
which can be obtained in Metazoa, without any co-ordination, by a mere 
appropriate arrangement of cells, which are differently developed accord- 
ing to their function. And yet, the evolution is soon limited, because 
the cells of the organism are not connected in such a way as to enable 
them to conduct stimuli from one cell to another ; in other terms, because 
they are destitute of the principle the significance of which culminates 
in nervous tissue.” 
The second chapter deals with Esperella segagropila (Johnst.) Tops., 
— its many synonyms, its structure, its degeneration after gemmule- 
forming, and so on. The third chapter discusses anisochelse and isochelas, 
their relations to one another and to other spicules. Finally, the authors 
describe the structure of the choanocytes, in regard to which they cannot 
confirm Bidder’s description of parallel rods in the collar, or of “ iris ” 
* Johns Hopkins Univ. Circ., xviii. (1898) pp. 1-3 (5 figs.). 
t Verk. k. Akad. Weteusch. Amsterdam, vi. (1898) pp. 1—51 (4 pis.). 
