2l6 J. S. HUXLEY. 



blood (mesenchyme) cells seen in dedifferentiated specimens of 

 the Ascidian Clavellina (cf. Driesch, '06). 



Up till 48 hours, the gut had remained apparently normal. In 

 these specimens, however, though the stomach was of normal 

 (Fig. 2, a) or even more than normal size (Fig. 2, c) the cesoph- 

 agus and intestine showed some degree of contraction. 



Extreme cases of dedifferentiation at 72 hours are shown in 

 Figs. 2, d and e. In Fig. 2, d, the general turgescence or tone, 

 and the transparent appearance of the aboral region is preserved, 

 but the oral region has rounded off, and all traces of the char- 

 acteristic form of the oral half of the animal, including the 

 ciliated band, have disappeared. The stomach too is affected, all 

 parts of the gut being now reduced, with thick epithelium. 



Finally in Fig. 2, e, we have a specimen with complete dedif- 

 ferentiation of the oral region. The aboral region, however, is 

 also markedly affected, and the whole body is filled with a nearly 

 opaque mass of cells, within which only faint traces of organs 

 are visible. The skeleton is reduced to two simple clubbed rods. 

 In this condition the animal much resembles a dedifferentiated 

 Clavellina, and the resemblance would externally be almost com- 

 plete if it were not for the presence of the spicules, which prevent 

 the retraction of the aboral region and the assumption of the 

 spheroidal form. 



At 96 hours, most of the specimens showed signs of partial 

 death. This manifested itself in the oral region by a disintegra- 

 tion of some of the tissue, and the protrusion of the skeleton. 

 The gut was in all cases contracted. The aboral region was usu- 

 ally contracted, but with no trace of disintegration. (Fig. 3, 

 a and b.} Most of them were transferred to sea-water. Those 

 that remained in the solution were all dead after 120 hours, with 

 aboral as well as oral disintegration, but very little or no disin- 

 tegration of the gut. Slight movement due to ciliary action, and 

 occasional contractions of the oesophagus were seen up to 96 hours. 



One interesting occurrence was noted after 72 hours. Two 

 plutei had grown together, the left anal arm of one having com- 

 pletely fused with the aboral region of the other, the skeletons 

 of the two individuals overlapping in the common region (Fig. 



