318 JULIAN 8. HUXLEY 
roughly the course of events in restitution-bodies in Sponges. 
It is clear, however, that in Sycon we have an admirable 
material for qualitative experiment, as to the rdle of size of 
masses, the proportion of the tissues in the mass, the coherence 
of cells, their mutual attraction, &e. 
The elucidation of these problems will need many workers, 
and it is hoped that others may be induced by the facts here 
set forth to take up the work. 
Meanwhile two tendencies should be noticed. ‘The first is 
a tendency to discuss the results from a morphological stand- 
point. This is shown, e.g., in Wilson’s discussion of results. 
He compares the development of the restitution-masses in 
detail with that of normal development, and goes so far as to 
apply the term ‘ yolk’ to the central syncytial portion which 
remains in the middle of the masses while the two layers are 
differentiating. This, and indeed his whole discussion, though 
of great interest, seems to me to be puttimg the cart before the 
horse. We should rather expect to find some of the causes deter- 
mining the presence and form of the normal yolk by examiming 
the mode in which the abnormal conditions of a restitution- 
mass influence the internal cells, rather than vice versa. 
A word is also in order as to the use of the terms ‘ normal ’ 
and ‘abnormal’. Abnormal is often used as if it were synony- 
mous with pathological. This is not the case in any of the forms 
of restitution-mass here described (until we reach degenerative 
change at the close of their history, this being due to lack of 
nutriment and to laboratory conditions). Deditferentiation, 
ageregation, sorting-out, &¢., are all perfectly healthy pheno- 
mena. 
11. Summary or Rzsuurts. 
(Including those recorded in previous papers.) 
1. Various methods can be used to dissociate the tissues of 
Calcarea Heterocoela. 
2. Mixture of the various types of cells in normal proportious 
may lead to the formation of normal regenerates, resembling 
post-larval Sycon, with spicules, osculum, and pores. 
