6 BRITISH HYDROID ZOOPHYTES. 



inner layer of cells ("endoderm"). The latter 

 differ in character from the former, the 

 endoderm cells being capable of throwing out 

 and withdrawing lobular processes (" pseudo- 

 podia "), and also others which are lash-like 

 (" flagella "). These two layers of cells are 

 separated by a fine membrane which differs 

 from the middle layer (" mesoderm") of the 

 sponges, and other groups, in being 

 non-cellular and having no structure. It is 

 known as the (" mesogloea "). 



No through alimentary Canal. 

 From the sack-like nature of the body, it will 

 be noted that there exists no through 

 alimentary canal such as we find foreshadowed 

 in the higher Coelenterates, and well-marked 

 in the Echinoderms. The base of the body of 

 the animal is used for attachment, or, as a 

 surface by which to crawl. 



No Organs of Sight, etc. This 

 description applies to the polypite phase only 

 of the Hydroid career, in which stage sense 

 organs (organs of sight, etc.) such as are 

 found in another the Medusa phase are 

 wanting, as also certain "pores" which 

 subserve excretion. 



