Mil INTRODUCTION. 



long as the vital energies are unexhausted. Hut the cells 

 are not mere isolated chambers placed side by side and 

 connected one with the other as portions of a continuous 

 structure, like the bricks in a house, but are united in a 

 much more intimate and vital way. Their soft contents 

 are in direct connexion no less than their external sur- 

 faces ; and as the structure by means of which this con- 

 nexion is maintained belongs to the system of the ectocyst, 

 it may be noticed here. 



In the outer wall of the cell (amongst the Cheilostomata) 

 certain spaces are met with in various positions, which 

 are composed of thinner material than the rest of the 

 ectocyst, and are pierced by one or more very minute 

 perforations (Woodcut, fig. iii. c-p). These thin perforated 



Fig. iii. 



Membranipora membranacea. Wall of zocecium. 

 cp. Communication -plates. 



plates occurring in the cell-wall have been named by 

 Reichcrt " Roscttcnplatten"*; but as this term cannot 

 be very aptly rendered into English, I shall distinguish 

 them as communication-plates. Amongst the Ctenosto- 

 mata we find their equivalent in the diaphragms closing 

 the cells at their base, and separating the internodes of 



* " Vergleichende anatomisehe Untersuchungon ii. Ztioliotryon 

 Elirenberg, von Karl B. Beichert," Abhiimll. d. kdnigl. Akad. d. V> 

 schaftcn zu Berlin, 1K<;<), p. LT.7. 



