164 
Journal of the Mitchell Society [ December 
the surface a thin membrane with underlying connective tis- 
sue (collenchyma). Flagellated chambers make their appear- 
ance in great abundance. Canals appear as isolated spaces 
which come to connect with one another. Short oscular tubes 
with terminal oscula develop as vertical projections from the 
flat incrustation. If the incrustation be of any size it pro- 
duces several such tubes. The currents from the oscula are 
easily observed, and if the cover glass be mounted in an 
inverted position on a slide the movements of the flagella of 
the collar cells may be watched with a high power (Zeiss 2 
mm.). This degree of differentiation is attained in the 
course of six or seven days when the preparations are kept in 
laboratory aquaria (dishes in which the water is changed 
answer about as well as running aquaria). Differentiation 
goes on more rapidly when the preparation is hung in the 
open harbor in a live-box (a slide preparation inclosed in a 
coarse wire cage is convenient). Sponges reared in this way 
have been kept for a couple of weeks. The currents of water 
passing through them are certainly active and the sponges 
appear to be healthy. In such a sponge spicules are present, 
but some of these have unquestionably been carried over from 
the parent body along with the squeezed out cells. 
The old question of individuality may receive a word here. 
Microciona is one of that large class of monaxonid sponges 
which lack definite shape and in which the number of oscula 
is correlated simply with the size of the mass. While we 
may look on such a mass from the phylogenetic standpoint 
as a corm, we speak of it as an individual. Yet it is an indi- 
vidual of which with the stroke of a knife we can make two. 
Or conversely it is an individual which may be made to fuse 
with another, the two forming one. To such a mass the ordi- 
nary idea of the individual is not applicable. It is only a 
mass large or small having the characteristic organs and tis- 
sues of the species but in which the shape of the whole and 
the number of the organs are indefinite. As with the adult 
so with the lumps of regenerative tissue. They have no defi- 
niteness of shape or size, and their structure is only definite 
