I20 ANATOMY AND DEVELOPMENT OF THE ECHINODERMS 



In the Echinoderm there is one larval-zooid and one Echinoderm- 

 zooid — the " individual " would be incomplete without either. 



But in the Cyana;a the single Scyphistoma-zooid developes perhaps 

 twenty Cyanaea-zooids, any one of which would have been sufificient to 

 complete the individual. 



The development of the hundreds of polypes of a Sertularian 

 appears to be referable to a similar law. Nay, the "generation by 

 gemmation " of a Hydra or a simple Ascidian, and the fi.ssion of a 

 Alicrostomum, .seem, strictly speaking, to be phjenomena 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 Aliiller's researches, of A\-hich our imperfect 

 notice can give no idea, — it is the singular candour and philosophic 

 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 necessary to make pretty hypo- 

 theses 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 investigation should 

 be conducted, we cannot do better than refer him to the ^\•orks whose 

 titles head this Report — they are models. 



EXPLAN.\TIO\ OF PLATE 1. [Plate 12] 



The figure.s numljered with the Arabic numerals all represent really existing forms, and 

 are taken, with the e.xception of figures 8 and 9, from Professor Muller's memoirs. The 

 "calcareous rods " are omitted for the sake of clearness. 



The figures numbered with the Roman numerals on the other hand are all to be con- 

 sidered merely as diagrams. They represent what the Echinoderm-larvte would be, if they 

 were, as it were, straightened out and reduced to their simplest elements. 



Fig. 1.'^ is given in order to show how a symmetrical Annelid-like lar^"a, fig. I., may by 

 development of some of its parts at the exjjense of others become converted into the Ophiura- 

 larva, fig. L 



Fig. I. Ophiura-larva L The corresponding diagram. 



Fig. 2. Echinus-larva with " epaulettes'' IF Ditto. 



Fig. 3. Echinus-larva w ith spines viewed from 



behind III. Ditto. 



P'ig. 4. Asterias - larva {Bipinnaria)^ very 



young I\", Ditto. 



j5;'(7i77?'t7/£2T/(7, an Asterias-larva W The diagram only is given 



