AXATOMV AND DEVELOPMENT OF THE ECHINODERMS lO/ 



made out, so that points of comparison with the embryological ph^eno- 

 mena to be described subsequently are wanting. One thing however 

 appears evident, \'iz. that, as in the other forms, the axis of the starfisli 

 is oblique to the axis of the larva from which it proceeds. 



The larvae whose development has been observed by Prof Muller 

 are widely different. 



These larvae may be reduced to two kinds : 1st, those of the 

 Ophiuridje and Echinidae (fig. i, 2, 3) ; 2nd, those of the Asteridae and 

 Holothuriada; (fig. 4, 5, 6, 7). 



I. The larva; of the Ophiurida; and Echinidae are somewhat hemi- 

 spherical bodies, having one edge of their truncated side prolonged 

 into a single flat and wide process, which carries the mouth and 

 oesophagus. 



On the hemispherical portion — not at the extremity, but on the side 

 opposite to that which is prolonged into the wide process — is a circular 

 anus. The oesophagus leads from the mouth, which looks in the same 

 direction as the anus, and opens into a globular stomach placed in the 

 hemispherical portion of the larva ; a short intestine runs from this 

 at right angles with the direction of the oesophagus to the anus. 



The extremity to which the mouth is turned may be considered 

 anterior, the anal side inferior, and it is this position which the animal 

 has in swimming.^ 



In this general description of the form of the larvae, however, some 

 most important and characteristic features have been omitted. These 

 are, the calcareous rods which form a sort of internal skeleton or frame- 

 work, and the ciliated fringe which is the organ of locomotion. 



The rods are four, eight, or more in number ; they run forwards, 

 diverging from the most convex or posterior portion of the hemi- 

 spherical part of the larva, and still clothed by the substance of the 

 larva, form processes of a considerable length : some of them pass 

 through the margins of the hemispherical part of the larva, some run 

 through and support the buccal prolongation.^ 



The ciliated fringe is a sort of ridge, thickly covered with large 

 cilia (which however do not exhibit the wheel motion), which forms 

 the edge of the flat anterior side of the hemispherical part of the larva 

 and of the buccal prolongation. It therefore passes above the mouth 

 and before the anus, completely encircling the body in an oblique 

 manner. It is continued forwards on one side and back on the other, 



1 These determinations of anterior and posterior, &c. are altogether different from those 

 of Prof. JMiiller. The mode of description adopted by the latter is quite accidental, and we 

 have changed it to make the general homologies more clear. 



^ See the figure given in the ' Annals,' ante, vol. xix. 



