106 



POPULAR ILLUSTRATIONS OF 



great points as we go on in order that those who take an interest 

 in these illustrations may mark, learn, and inwardly digest the 

 great plan upon which living structures are built up. Henceforth, 

 then, in the scale of life we shall find a free stomach in the subject 

 of our study. It is the first truly differentiated organ we have 

 hitherto met with ; and this fact will be impressed on the reader's 

 mind evermore if he will note therein that this occurs in the 

 Actinozoa, and that the type of this division is the well-known sea- 

 anemone of our coasts. 



But, to assist his memory, I will give diagrams illustrating the 

 difference in this respect between the Hydrozoon and the Actinozoon. 



iS 



d 



Fig. 143. 

 Longitudinal Section of Hydrozoon. 



a, mouth b, stomach c, endoderm d, ectoderm e, tentacles. 



Fig. 144. 

 Transverse Section of same. 



Fig. 145. 

 Longitudinal Section of Actinozoon. 



Fig. 146. 

 Transverse Section of same. 



, mouth 6, stomach c, endoderm d, ectoderm e, tentacles-/, lamellar plates, or 

 mesenteries, which divide the somatic cavity into what are termed/, loculi- h, ova or 

 germs -sr, body containing thread cells i, opening of stomach into () the somatic 

 cavity. 



Fig. 143 is a longitudinal section of a Hydrozoon, and Fig. 144 a 

 transverse section of the same ; while Figs. 145 and 146 represent 

 similar sections of the Actinozoon. The letters indicate the same 

 parts in each figure. Now, mark that the stomach (b) is in the 

 Hydrozoon hollowed out, as it were, of the body substance, while it 



