230 



opening, afterwards becoming the anal opening ; at this time, how- 

 ever, serving both for taking in and rejecting the food). From 

 the upper extremity of the digestive cavity next project two lohes 

 (w, w', Fig. 94, m, mouth). These separate from their attachment 

 and form two distinct hollow cavities («?, w 7 , Fig. 95, a, d, c, di- 

 gestive system ; v, vibratile chord ; m, mouth). Here begins the 

 true history of the young starfish, for these two cavities will de- 

 velop into two water-tubes, on one of which the back of the star- 

 fish, that is, its upper surface, covered with spines, will be devel- 

 oped, while on the other, the lower surface, with the suckers and 



Fig. 88. Tig. 89. Fig. 90. Fig. 91. 



tentacles, will arise. At a very early stage one of these water 

 tubes (w 1 Fig. 96) connects with a smaller tube opening outwards, 

 which is hereafter to be the madreporic body (6, Fig. 96). Almost 

 until the end of its growth, these two surfaces, as we shall see, 

 remain separate and form an open angle with one another ; it is 

 only toward the end of their development that they unite, enclos- 

 ing between them the internal organs, which have been built up in 

 the meanwhile. 



"At about the same time with the development of these two 

 pouches, so important in the animal's future history, the digestive 

 cavity becomes slightly curved, bending its upper end sideways 



