10 Prof. Miiller on the Anatomy and Development 



very small cells are imbedded^ is seen lying like a mantle upon 

 the dorsal side of the stomach. 



The sac becomes developed into a rosette of five ca3ca, the first 

 fomidation of the water- vascular system. 



The uiantle-likc mass curves over and covers in the stomach 

 and foundation of the tentacles like a cap, widely open below. 

 The dorsal pore becomes invested by it, and it extends round 

 the anus ; but the oesophagus remains outside it (Diag. XI.). 



A crest or elevation now appears on the mantle-like mass, and 

 runs obliquely over it in a curved line, whose ends become even- 

 tually united. It then forms the margin of the starfish. 



What lies beneath this thickened margin belongs to the dor- 

 sum of the starfish, what lies above it to its ventral surface. 



The young starfish now attains a diameter of yth of a line, 

 becomes slightly pentagonal, and retains only a narrow connexion 

 with the Bipinnaria. 



The digestive canal, and with it the rosette-like rudiment of 

 the water-vascular system, becomes turned so as to present the 

 latter towards the ventral surface of the starfish, at that point 

 where its mouth is subsequently formed. The tube which con- 

 nected the rosette with the pore, which is now imbedded in the 

 dorsal surface of the starfish, receives a calcareous deposit and 

 becomes the sand-canal, while the " pore " is converted into the 

 madreporic plate. 



The oesophagus of the larva is obliterated, whilst its rectum 

 projects as an anal tube subcentrally from the dorsal surface of 

 the starfish (Diag. XIII.). 



The slightest touch now separates the starfish from the larva 

 in which it was developed ; the former sinks to the bottom and 

 creeps by the aid of its newly-developed feet ; the latter swims 

 about as before for some time, but eventually perishes. 



In the Echinidaj the process is essentially the same. An in- 

 ternal diverticulum of the integument of the larva is formed, but 

 from a soQiewhat different spot*, namely in front of the ciliated 

 fringe and on one side. It is connected with a vesicle which lies 

 close against the oesophagus, and from which the water-vascular 

 system is developed. 



At this place the shell of the Echinus subsequently makes its 



* It is remarkable that in the Asterid-larvee, while the cleveloi)meiit of 

 accessoiy ciliary processes, &c. takes place in the pre-trochal dorsal region, 

 the bud of the Echinoderni is developed from the post-trochal region. In 

 the Echinus-larva; we have just the reverse — the bud is developed from the 

 pre-trochal region (" below the lateral arch of the ciliated band," Miiller), 

 while the processes, &c., as we have seen, are developed from the post- 

 trochal region. The Ophiurae appear to present the same relations as the 

 Echinida;, though Prof. Miiller has not been able to make out the point 

 with certaintv. 



