454 



TUNICATA. 



number of parts, each of whicji develops into a young Ascidian. 

 The first sign of development is shown in a widening of the proximal 

 end (K) of the ectoderm-tube (segment of the epicardial sac) which 

 lies in every segment. This proximal dilation is the rudiment of 

 the whole alimentary canal of the young animal. The non-dilated 

 part of the entoderm-tube becomes the epicardial tube of the ycung 

 individual. The heart of the parent-animal that has remained in 

 the distal segment now degenerates. Somewhat older colonies 

 (Fig. 228) are of a different shape. The young animals, which 

 originally lay in a row one behind the other, show a tendency to 



FIG. 228. Two young colonies of Amaroutium (after KOWALEVSKY). A, younger, 

 B, older stage, a, parent-animal ; b, an advanced bud ; c,, younger buds. 



shift upward within the test towards the parent-individual, and the 

 whole colony thus becomes broader and shorter. The parent-indi- 

 vidual now begins to develop, through regeneration, a new heart 

 and post-abdomen (Fig. 228 A, a). The daughter-individuals in the 

 figure seem to be at different stages of development. One of them 

 (b) exhibits the almost perfect organisation of the adult Ascidian, 

 while the three others show the rudiments of the different parts of 

 the body, but these are very slightly developed. In all these young- 

 individuals the post-abdomen is still comparatively short. Only 

 later (Fig. 228 B) does it grow out to a greater length, and come 



