The septal muscles are without a lumen and they each occupy a 

 tube in the jelly. The --vail of tliis tube is lined by a layer 

 of longitudinal muscle fibres and within these there is a gran- 

 ular substance with scattered nuclei : Towards the end of the 

 stem the muscles gradually become smaller and, the jelly becom- 

 ing very thin, they are closely applied both to the entoderm 

 and ectoderm. The ectoderra cells in this region become very 

 flat- and are covered by a cuticula, and there is now a marked 

 differentiation between the entoderm of the calyx and that of 

 the stem. 



This is better shown in a longitudinal section of a little 

 older larva. Fig. 37. The epithelium lining the proboscis is 

 now very different from that covering its exterior. The lin- 

 ing epithelium is thick and composed of crowded narrowly colum- 

 nar cells. At the septa this epithelium passes abruptly, and 

 in the gastric pouches more gradually, into the entoderm of the 

 calyx. This is likewise a deep columnar epitheliiun but the 

 cells are larger, are vacuolated at tlieir bases, and many ap- 

 pear to be gland cells containing coarse granules at their free 

 ends. At the plane where the calyx joins the stem there is a 

 rather sudden transition from this character of epithelium to 

 the large, clear cells of the stem. The stem is hollow near- 

 ly to its base. The solid entodermal core of the tentacles 



- 36 



