18 On the Anatomy and Development of the Echinoderms. 



by gemmation " of a Hydra or a simple Ascidian, and the fission 

 of a Microstomum, seem, strictly speaking, to be phenomena of 

 the same kind. 



As in these cases, however, it is impossible when once the 

 gemma is separated from the parent stock to distinguish it from 

 a true individual, it may seem pedantic and unnecessary to insist 

 upon the distinction. 



In concluding, we cannot refrain from remarking upon one 

 character of Professor Muller's researches, of which our imper- 

 fect notice can give no idea, — it is the singular candour and phi- 

 losophic impartiality of the writer. In the course of five years, 

 much that seemed probable at first, had, later, to be rejected — 

 much that seemed certain, to be overthrown. It was often neces- 

 sary to make pretty hypotheses give way before stubborn facts — 

 to re-examine conclusions that had seemed unquestionable. 



If any one be curious to know how this has been done, and 

 desire at the same time to learn in what spirit scientific investi- 

 gation should be conducted, we cannot do better than refer him 

 to the works whose titles head this Report — they are models. 



EXPLANATION OF PLATE I. 



The figures numbered with the Arabic numerals all represent really ex- 

 isting forms, and are taken, with the exception of figures 8 and 9, from 

 Professor Muller's memoirs. The u calcareous rods " are omitted for the 

 sake of clearness. 



The figures numbered with the Roman numerals on the other hand are 

 all to be considered merely as diagrams. They represent what the Echi- 

 noderm-larvse would be if they were, as it were, straightened out and re- 

 duced to their simplest elements. 



Fig. I. a is given in order to show how a symmetrical Annelid-like larva, 

 fig. I., may by development of some of its parts at the expense of others 

 become converted into the Ophiura-larva, fig. 1 . 



Fig . 1 . Ophiura-larva ' I . The corresponding diagram . 



Fig. 2. Echinus-larva with " epaulettes " II. Ditto. 



Fig. 3. Echinus-larva with spines viewed III. Ditto. 



from behind. 



Fig. 4. Asterias-larva (Bipinnaria), very IV. Ditto. 



young. 



Brachiolaria, an Asterias-larva... V. The diagram only is given. 



Fig. 5. Tornaria, probably an Asterias- VI. The corresponding diagram. 



larva. 



Fig. 6. J* Auricularia, the Holothuria- VII. \ jy , , 



Fig. 7. 1 larva in its two forms VIII. J 



In all the figures of larvae the mouth and anus are indicated by the letters 

 m and a, and the cilia are disproportionately large so as to render the 

 "fringes" and " bands " evident. 



The Diagram No. I. is similarly lettered, and all the other diagrams have 

 their anterior and posterior extremities in a position corresponding to it. 



