224 SCIENCE PROGRESS. 



to be beyond all doubt. We miss in all his figures any 

 indication of cell outlines, and he does not seem to have 

 made use of methods calculated to show them up. Had 

 he done so it is possible that his groupes polynuclees might 

 have turned out to be only ciliees closely packed round 

 granular amoeboid cells, which is indeed the impression 

 some of his figures give. The syncytium formed by the 

 undevoured ciliees seems equally doubtful. Sections of 

 greatly contracted tubes of Ascetta clathrus prepared by 

 ordinary methods show a similar closely packed mass of 

 cells, without apparent cell outlines, in the interior. There 

 is no reason to suppose, however, that cell boundaries are 

 really wanting, for each cell is derived from a single collar 

 cell, and becomes such again when the sponge expands to 

 its normal condition. Moreover, by suitable methods of 

 maceration the cells in this apparent syncytium can be 

 isolated from one another. 



The researches of Maas and Delage, complete as they 

 are, leave many interesting questions to be decided by future 

 investigators, questions upon which it is impossible to pro- 

 nounce more than an opinion meantime. If the present 

 writer, after having been an eye-witness of Dr. Maas's 

 investigations, and having had the opportunity of studying 

 his preparations, is more inclined on that account, as well as 

 on general grounds, to take Dr. Maas's view of the ques- 

 tions at issue, it is from no wish to detract from the value 

 of the beautiful investigations of M. Yves Delage. And, 

 as we have seen, our authors are entirely agreed upon more 

 fundamental points, so that, to briefly recapitulate, we may 

 draw up the following typical course of development for a 

 siliceous sponge. 



The segmentation is unequal, leading to the formation 

 of micromeres at one pole and macromeres, containing the 

 yolk, at the other. Later on the micromeres are found more 

 or less completely surrounding the macromeres. The micro- 

 meres become a ciliated epithelium, and the larva is hatched 

 consisting of two layers : ( I ) an external layer of flagellated 

 cells, (2) an inner mass of various kinds of granular cells, 

 which are either completely internal, or protrude posteriorly, 



