Professor Eerdman on the Structure of Sarcodictyon. 47 



The gastric tube which is continued down from the elongated 

 mouth opening (PL I., Fig. 12) is flattened so as to be irregularly 

 elliptical in transverse section. At one end of the longer axis 

 are placed the t^yo mesenteries ^Yhich have their muscular faces 

 turned towards each other, while the two mesenteries at the 

 other end have the corresponding faces turned from each other. 

 Hence the inter- mesenteric chamber at the one end contains 

 two pinnate muscles, and that at the other end contains none 

 (see PL I., Fig. 18). The remaining six inter-mesenteric 

 chambers — three on each side — have each one pinnate muscle. 



The wall of the gastric tube is thick and is much folded upon 

 itself, both vertically and horizontally (PL I., Fig. 13). It is 

 lined by a layer of ectoderm continued through the mouth 

 opening from the ectoderm lining the invaginated tube. Fig. 8 

 on PL III. shows half of the gastric tube in transverse section 

 highly magnified. The ectoderm layer {ec) is seen to be 

 thrown into ridges and grooves, and is formed of long columnar 

 cells closely placed. No cilia were visible in my specimens, 

 although they are probably present in the living condition. 

 The " siphonoglyphe " was not distinct, probably on account 

 of the corrugation of the wall, but I recognised traces of it 

 here and there in a few of the sections, by means of the very 

 long cilia which were still attached to the cells. 



Outside this epithelium is a thick layer of mesoderm formed 

 of an inner mass of muscular fibres, and an outer comparatively 

 narrow homogeneous band {mes) which is continuous with the 

 mesoderm of the mesenteries. This outer structureless layer 

 of mesoderm has a narrow line of muscle fibres on its outer 

 side just beneath the endoderm, and these fibres are con- 

 tinuous with the muscles on the sides of the mesenteries. 



The endoderm forming the outermost layer of the gastric tube 

 is like the endoderm lining the body wall, and is continuous 

 with the same layer of cells on the faces of the mesenteries 

 (PL III., Fig. 8). In such cases as the one represented in 

 Fig. 4 on PL III., where the wall of the gastric tube has 

 been cut several times in the same horizontal plane, the 

 different transverse sections are exactly similar, the second 

 and third being merely repetitions of the first or inner one so 

 far as structure is concerned. 



