RESTITUTION-BODIES AND FREE TISSUE-CULTURE IN SYCON 311 
Lhr. 55m. No flagella. Disintegration starting in all. 
18 hrs. 45m. Masses present, but more disintegrated than C. 
n 
E. 100,000 Hes. 
50m. Collar-cell blow-outs no longer visible. One dermal blow- 
out unaffected. Two masses with a few flagella moving (slow 
or spasmodic). Flagella somewhat shortened. Masses with 
irregular outlines. 
Thr. 50m. All cells rounded off, total disintegration of masses 
starting. 
18 hrs. 30m. Completely disintegrated into groups of one to twenty 
dead cells. 
rh) n ‘ 
E600. o> = 
40m. No collars or flagella. Blow-outs burst, contracted, or 
disappeared. Masses with irregular outlines. 
1 hr. 50 m. and 18 hrs. 30m. As E, 
10. Discussion. 
(a) Dedifferentiation. Position and Fate. 
Wilson, in his work on dissociation and subsequent regenera- 
tion in Monaxonid sponges, left the question entirely open as 
to whether regeneration was due wholly to the ‘ totipotent ’ 
amoebocytes, or whether the differentiated tissue elements 
underwent a process of * despecialization ’ (dedifferentiation) 
into an ‘indifferent or totipotent state’, after which they 
took their shares in restitution. He does not seem to have 
envisaged the possibility of the differentiated cells sharing in 
the restitution-process without undergoing total dedifferentia- 
tion. In his later paper, on dissociation and restitution in 
Hydroids (16), he returns to the subject, and decides that in 
these forms, where undifferentiated cells form but a fraction of 
the normal body, the differentiated tissue-elements definitively 
become despecialized * to form masses of totipotent regenerative 
tissue ’. The cells in these masses later differentiate in accor - 
dance with their position, the outer cells forming 
ectoderm, the central core endoderm. ‘This is, of course, in 
accordance with Driesch’s well-known dictum that the fate 
