4 THE POPULAR SCIENCE MONTHLY. 



the column. These six compartments are made by as many radiating 

 vertical plains, whose edges on the one side are in contact with the 

 inner walls of the column, and tlie edges on the other side touch upon 

 the outer walls of the stomach. Between these compartments are 

 others of less capacity. It is noticeable that these are, in like manner, 

 formed of vertical plains, of different widtlis ; and, further, that they 

 are only attached on one edge, and that to the inner walls of the 



Fig. 2. Ckoss-Sectiok op an Actinia-Stem. 



great column, that is to say, they do not connect with the stomach. 

 To understand the relation of these different walls of the compart- 

 ments to the entire structure, a glance at the diagram will suffice, 

 when it is borne in mind that the transverse section, thus represented 

 gives also a section of the inner cylindrical sac, or stomach. 



The upright walls of these compartments which we have described 

 are known in science by the name mesenteries. Of what use are 

 they ? The most obvious service they perform for the animal when 

 erect is, as we think, the stiffening of the structure. And this is done 

 at will, as if it were a sort of erectile tissue. Now, as the cardinal 

 plains connect both the inner and the outer cylinder, that is, the 

 stomach and the column, it will be seen that the efficiency in the 

 direction of imparting strength is considerable. The column is by so 

 much the more strengthened, as it has the more of these upright planes 

 or septse attached to it by one of their respective edges. 



But it is in these compartments, and on the mesenteries them- 

 selves, that the origin of life for the actinia's progeny begins for 

 there the ova and the spermatozoa are found. On the mesentery- 

 walls are borne in series certain reddish bands. These are the repro- 

 ductive organs, and contain the ova and the spermatozoa. Generally 

 actiniae are what the botanists call dioecious ; that is, the ova are 

 found in an individual that we may call the female ; and the sperma- 

 tozoa in one that we may in like manner call the male. As to the 

 time, and even the method of propagation, mother actinia is very 

 capricious, there being, so far as our observations may determine, no 

 regularity, but at the right time doubtless, for her convenience, the 

 actinia evicts her young. Usually these are discharged at the mouth. 



