THE ANATOMY OF ALCTONIUM DIGITATUM. 375 



their free ends. It is possible that those cells (such as fig. 28, 

 a, c, 0, n) which do not show a flagellum may have lost it during 

 the preparation and maceration of the specimen. 



The muscular portion of the fibre is homogeneous and trans- 

 parent. It is usually branched at the extremities. Although 

 most of the cells possess a muscular portion, there are un- 

 doubtedly some cells in the endoderm which do not. The cell 

 represented in fig. 28 /is a type of cell very frequently met 

 with in these maceration preparations. It possesses two long 

 protoplasmic processes. 



A few cnidoblasts may be seen in such preparations of the 

 endoderm-cells, and are represented in fig. 28, h and k ; 

 but it is very probable that they have been swallowed with the 

 prey, and are not of endodermic origin. 



Although the study of macerated preparations reveals many 

 points of great interest which cannot be seen satisfactorily in 

 any other way, it has the disadvantage of giving no evidence of 

 the true relationship of the cells to the organs of the body. 



The endoderm is not precisely the same in all parts of the 

 coelenteron, and consequently it is necessary to supplement our 

 study of macerated specimens by a study of carefully prepared 

 sections through difi'erent parts of the body. 



In the lower part of the coelenteric tube the endoderm has a 

 very vacuolated appearance. This is due, not to the occurrence 

 of intra-cellular vacuoles, but to great gaps between the endo- 

 derm-cells. 



The individual cells are thinner than they are in other parts 

 of the body, and loosely connected together in groups which 

 are separated from one another by considerable rounded 

 spaces. 



The character of the endoderm in this region is very similar 

 to that described by Lankester as occurring in the proximal 

 third of the gastric tube of Limnocodiura (27). 



If sections be taken through the upper parts of the tube in 

 the region of the ventral mesenterial filaments, the endoderm- 

 cells (fig. 23) are seen to be much more closely set, and to con- 

 tain larger granules. 



VOL. 37, PAET 4. — NEW SER. C C 



