132 Proceedings of Royal Society of Edinburgh. [sess. 
The tube and funnel are both surrounded by a thick mass of 
blood corpuscles. 
As resards the organs of the ectoderm and mesoderm, Adino- 
o o 
trocha may be regarded as consisting of three segments, one pre- 
oral and two post-oral. 
The organs of the endoderm have yet to be referred to. 
The mouth leads by a short oesophagus into a wider stomach 
region, and the front wall of this stomach is produced forwards as 
a pair of hollow diverticula, lying laterally on each side of the 
Fig-. %. 
Fig 3. — Longitudinal horizontal section 
of Actinotrocha , in front of fig. 2. 
Fig. 4. — Notochordal diverticulum 
of Actinotrocha, as seen in fig. 3, 
but with high power. 
oesophagus (fig. 3, n-c.). These two coeca arise from the region of 
the collar, that is, the part of the gut which is surrounded by the 
collar cavities, and they protrude into the collar space, almost 
coming into contact with the outer wall at the apex of the 
tentacular ring. The most superficial examination of sections 
shows that they cannot be regarded as glandular, but that 
the constituent cells have been metamorphosed into vacuolated 
tissue.* The process of vacuolisation proceeds from without 
inwards, and in the latest stage observed there is always a 
part of the wall lying on the inside , which had a number of 
nuclei lying in a mass of cell-protoplasm, in which the vacuoles are 
* The vacuoles do not stain with borax-carmine or haematoxylin. 
F>s4- 
