THE .LOWER FORMS OF LIFE. 107 



is seen suspended into the somatic cavity in the Actinozoon. The 

 stomach of the former is only separated from the external world 

 by the endoderm (c), the ectoderm (d), and the intervening sarcode. 

 In the latter there is seen at k a wide space between the free 

 depending stomach () and the body wall at c d. And this space is 

 found to be divided into partitions, which are occupied by certain 

 organs (g h), and communicate above with the hollow tube called 

 the tentacle, as diagrammatically represented at e. Now, a brief 

 examination of these partitions and organs will reveal to us the 

 morphology of the Actinozoon, and show us how far upwards we have 

 now reached in the scale of organised nature. 



From the mouth (a, Fig. 145) is seen dependent the stomach (5), 

 in a kind of hollow formed between the inner plate of the partitions. 

 At i the stomach opens into the somatic cavity (k), where the 

 digested food serves the purposes of nutrition, the useless reliquiae 

 being returned through the same opening. 



Now, in this lowly and beautiful flower-like animal there are 

 shadowed forth structures which are fully developed in the higher 

 class of animals. Let us illustrate this : 



The body wall (c d, Fig. 145) consists of two membranes, the ecto- 

 derm (d) and the endoderm (c), and between them, as shown by the 

 lines, are two distinct classes of muscular fibres, by which the animal 

 contracts or dilates itself at pleasure. The ectoderm (d) is, however, 

 itself divisible into two membranes, the outer one resembling the 

 epithelium, and the under layer the derma, or true skin of the 

 higher animals ; and between these layers of skin are imbedded 

 vast numbers of thread cells and the pigment granules by which the 

 beautiful colours of the anemone are produced. The endoderm (c) 

 may also be separated into two layers, one of which is in contact 

 with the muscular structure ; the other is free, and forms one of the 

 boundaries of the partitions, as seen at c (Fig. 146). Both the endo- 

 derm and ectoderm have their free surf aces covered with the hairlike 

 bodies, which I described in a former chapter, termed cilia. The 

 stomach is a simple thin sac, also of two layers, having its inner 

 surface covered with cilia (b, Fig. 145). 



In the muscular structure between the endoderm (c) and the ecto- 

 derm (d) we have a foreshadowing of that important part of animal 

 organisation which we know so well in our own bodies. There are 

 two kinds of muscle in this covering of the Actinozoa a longi- 

 tudinal series of fibres deeply seated, and a circular series, superficial. 

 Each of the partition walls (/, Fig. 146) has two muscles on its 

 surface, and the muscular fibres of the stomach enable the opening (i) 

 to close or open at the will of the animal, while the tentacles (e e) are 

 moved by similar structures. The contraction of the animal itself and 



