248 
thicker. It is very fibrillous and contains numerous protoplasma-poor 
cells. The small cinclides seem to be excavations from the endoderm 
as well as invaginations from the ectoderm. The circular muscles 
of the column are ordinarily developed. Their folds are not high, 
but very fine and numerous, here and there small parts seem to be 
Figs. 40, 41. Thoe vagrans. Fig. 40, Transverse section of sphincter, fig.41. Outer half of 
pennon in a mesentery of first order in the ciliated tract region. 
enclosed in the mesogloea, also between the insertions of the me- 
senteries. The mesogloeal sphincter (textfig. 40) is strong and wholly 
separated from the circular muscles of the column. In its upper 
part it filis out almost the whole breadth of the mesogloea and 
diminishes by degrees in breadth. It is mostly reticular, in the 
outer and upper part more alveolar. The muscle meshes are mostly 
fine, in the upper and lower part of the sphincter larger (textfig. 40). 
