DIFFEEENT TYPES OF LARV.E.. 73 



fishes.] There is still another type of Echinoderm larvne,. which in all 

 probability are the larvte of Starfishes, viz. the Tornaria type. [For 

 the history of Tornaria, which has been proved to be the embryo of Bala- 

 noglossus, see my paper in the Memoir of the American Academy, Jan. 1873, 

 where the relations of Balanoglossus and Tornaria to Echinoderms and their 

 mode of development are fully discussed.] In this type there is not the 

 excessive development of the ciliary chord into long, slender arms, charac- 

 teristic of the Brachiolaria ; there are only slight, wavy indentations, cor- 

 responding to the position of the arms of the Brachiolaria, as we find 

 them in the younger stages of the larva? (PI. III. Fig. 4; PL 11. Fig. 26). 

 In fact, this type of larva, in its adult condition, seems to be a permanent 

 embryonic type of the younger stages of the Brachiolaria. I would infer 

 from this that the Tornaria will probably prove to be the larva of Cteno- 

 discus, Astropecten, or Luidia, or of some Starfish with pointed ambulacral 

 suckers. Having had the opportunity to examine several of the Tornaria 

 type of larvae at Naushon, in different stages of development, I hope to 

 return to this subject at a future time. 



[The only important embryology relating to Echinoderms in general pub- 

 lished since the distribution of copies of this Memoir in 1864, is that of 

 Metschnikoff.* He has confirmed the explanation I had given of the mode 

 of development of the Echinoderm upon the surfiice of the water-tubes, 

 the spiral nature of the young embryo, the mode of development of the 

 water-tubes as diverticula of the original imaginated cavity, and the re- 

 sorption of the pluteus by the young Echinoderm in Starfishes ; he has 

 also been able to follow very carefully the mode of development of the 

 water-system of an Ophiuran, and showed its entire agreement with the 

 changes I have traced in the development of the Starfish as far as relates 

 to the formation of the abactinai system and the ambulacral system. 

 Although Metschnikoft' has added some new points to the development of 

 Echinoids, still the mode of formation of the original plates composing 

 the test of the young sea-urchin is not yet clearly shown, beyond the 

 very earliest stages. As far as relates to the development of Auricularia, 

 we can form a better idea than formerly of the nature of the change from 

 the Auricularia to the young Synapta ; and certainly in a general way this 

 development is different from the normal growth of some of the other 



* Studien iiber die Eatwickelung der F.rhinodermen und Ntmei-tinen, Mem. Aead. St. PetersD. 

 XIV. No. 8. 1869. 



