76 EMBRYOLOGY OF THE STARFISH. 



then attempts to prove, fiiriner, 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 praetrochal region. Any 

 one who has observed these larvae 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 Holothiirian Selenka], is 

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

 outer surface of opposite water-tubes, one of them forming the actinal, the 

 other the abactinal surface of the future Echinoderm. The hypothetical 

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

 larvae 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 St«arfish. [See 

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

 the WurmHirmige 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 larvae, as compared with the 

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

 Echinoderm larvae, 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 larva? is formed by the liquefaction of tlie interior 

 of the larva, wliile in the Echinod(Min larva? the digestive cavity is formed 

 by the bending in of the outer wall of the Inva itself The superficial 

 resemblance of Annelid larvae to those of P>liinoderms is due to the append- 

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



