of the Echinoderms. 5 



which the disc of the starfish is developed do not appear to have 

 been clearly made out, so that points of comparison with the 

 embryological phenomena to be described subsequently are want- 

 ing. One thing however appears evident, viz. that, as in the other 

 forms, the axis of the starfish is oblique to the axis of the larva 

 from which it proceeds. 



The larvae whose development has been observed by Prof. Mul- 

 ler are widely different. 



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

 Ophiuridae and Echinidse (fig. 1, 2, 3) ; 2nd, those of the Aste- 

 ridae and Holothuriadae (fig. 4, 5, 6, 7). 



1. The larvae of the Ophiuridae and Echinidae are somewhat 

 hemispherical 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 glo- 

 bular 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 in- 

 ternal skeleton or framework, and the ciliated fringe which is 

 the organ of locomotion. 



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

 wards, diverging from the most convex or posterior portion of the 

 hemispherical 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 j\ 



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 



* These determinations of anterior and posterior, &c. are altogether dif- 

 ferent from those of Prof. Miiller. The mode of description adopted by 

 the latter is quite accidental, and we have changed it to make the general 

 homologies more clear. 



f Sec the figure given in the ' Annals,' antr, vol. \ix. 



