624 W. B. HARDY. 



body. In Myriothela they occur in their greatest abundance 

 in the endoderm of the lower half of the tentacle-bearing 

 region. But they are also numerous in the middle region of 

 the body whence the blastostyles spring, and may even occur in 

 limited numbers in the endoderm of those structures near their 

 points of attachment. 



In the middle and lower regions of the body the endoderm 

 is to a certain extent different from that already described. 

 The villi, as a rule, become less muscular, while at the same 

 time their apical cells change their characters and become more 

 and more akin to the vacuolate cells. The endoderm of the 

 body-wall from which the villi spring, and which in the lower 

 tentacle-bearing region is composed of cells in no wise dis- 

 tinguishable from those lining the villi, changes its character 

 in the blastostyle-bearing region. There it is composed of 

 long columnar cells, each with a single nucleus, and each 

 composed of dense well - staining protoplasm free from 

 vacuoles. 



The endoderm maintains these characters in the foot; that 

 is to say, the villi, which here are of the nature of broad flange- 

 like folds, are covered by vacuolate cells with rarely a gland- 

 cell, while the endoderm of the body-wall is composed of the 

 deeply-staining columnar cells. At the extreme end of the 

 animal^ however, the supporting lamella ceases to exist, and to 

 a certain extent the limits between ectoderm and endoderm 

 become obscured, and a kind of growing-point to the creeping 

 stolon is the result. 



The endoderm of the blastostyles will receive special mention 

 later. To make this general account of the whole endoderm 

 complete, however, I will merely state here that the villi in 

 the blastostyles are low conical structures almost exclusively 

 composed of vacuolate cells. A few gland-cells lie scattered 

 in the proximal third of each blastostyle. 



Taking the most general view of the structure of the epithe- 

 lium lining the enteric space of Myriothela as described in 

 the preceding pages, we see that it may be divided into different 

 regions. These are — (1) An oral region characterised by the 



