76 EMBEYOLOGY OF THE STAEFISH. 



then attempts to prove, furtlier, that there is an intimate connection be- 

 tween the point where the young Echinoderm is developed, and the po- 

 sition of the rows of vibratile fringes ; Starfishes being, according to him, 

 developed in the postrochal and the Echini in the pra^trochal region. Any 

 one who has observed these larva) alive cannot fail to see that whatever may 

 be the position of these vibratile fringes, the young Echinoderm, whether it 

 be an Echinus, a Starfish, or an Ophiuran [also a Holothurian Selenka], is 

 developed in exactly the same spot on the sides of the stomach, upon the 

 outer sui'face of opposite water-tubes, one of them forming the actinal, the 

 other the abactinal surfoce of the future Echinoderm. The hypothetical 

 form of Huxley is indeed one which has never been observed, as in all 

 larvfe of Echinoderms the mouth and anus are always on the same side, 

 viz. on the lower surface of the larva. It is only during the first few days, 

 after hatching from the egg, that the so-called mouth is placed at one 

 end ; this, however, is not observed beyond the time when this open- 

 ing performs the double function of mouth and anus, and leads into a 

 very short digestive cavity. By the time the true mouth begins to be 

 formed, the future anus, which has served the purpose of mouth thus far, 

 has already changed its position to the lower side. The mouth is, in fact, 

 never formed at one extremity, but always in the centre of the lower 

 surface, and only some time after the anus, which performs the functions 

 of a temporary mouth. This has been demonstrated by Krohn and my- 

 self, with reference to the Echinus larvae, and I trust that the preceding 

 pages have shown it to be also the case with our common Starfish. [See 

 also Selenka for Holothuria.] The division into rings, of what Miiller calls 

 the Wurmfdrmige Asteridenlarve, is only an optical delusion, due to the 

 lines formed upon the abactinal surface during the closing of the pentagon. 



The radical difference in the mode of formation of the oesophagus, 

 stomach, and intestine, in the Echinoderm larvte, as compared with the 

 larva? of Annelids, a number of which, including those most resembling 

 Echinoderm larvte, I have examined myself, will, perhaps, be the strong- 

 est proof that they do not belong to one and the same type. The diges- 

 tive cavity of Annelid larvte is formed by the liquefaction of the interior 

 of the larva, while in the Echinoderm larvae the digestive cavity is formed 

 by the bending in of the outer wall of the larva itself. The superficial 

 resemblance of Annelid larvaB to those of Echinoderms is due to the append- 

 ages surrounding the mouth, while the principal appeirdages of the Echini 



