174 



specimen figured in PI. XXXI, Fig. 2 the six primary plates of the dorsal 

 side have appeared and three of the terminal plates have just begun to 

 develop, beginning with the posterior radius, as is evident from the relative 

 size of these three rudiments. On the ventral side no skeletal plates have 

 been formed as yet. There is not the slightest trace of a larval skeleton. 



In specimens 2^/2 days old (PI. XXXI, Fig. 3) the terminal plates have 

 been fully formed, the unpaired, terminal tentacle lying within it as in a 

 tube. (Although the skeleton has been dissolved in all the specimens of 

 this age preserved, this fact can be distinctly ascertained). Inside the first 

 formed pair of tentacles indications of another pair of much smaller out- 

 growths from the radial canals are seen. This is in accordance with the 

 interesting fact observed by Grave in Ophioderma brevispina, that the 

 buccal tentacles are formed after the second pair. The same observation 

 was also made by Krohn^) in a similar Ophiurid larva which was found 

 at Madeira. It seems highly probable that this is really the usual order 

 of appearance of the oral tentacles in Ophiurids. 



As stated above, the median band is nearly complete across the dorsal 

 side, while on the ventral side it is, of course, interrupted by the mouth 

 opening of the Ophiurid. The left part of the posterior band has developed 

 towards the mouth so that there are now three distinct bands reaching 

 the mouth edge, one to the right, two to the left side. The rest of the 

 posterior band remains at the right side of the posterior end. 



At this stage the larva evidently has reached its fullest development, 

 and it is worth mentioning that it was observed now to swim fairly actively, 

 while on the other hand, it could also now attach itself to the bottom 

 by means of its tubefeet, so firmly that it was hardly possible to wash 

 it off by means of a pipette. — Also in the stage of 40—45 hours the larvae 

 were observed now and then to swim free in the water. 



At the age of 6 days the anterior lobe of the larva is still distinct, with 

 its cihated bands, but it is very much shortened and evidently in the 

 course of being absorbed (PI. XXXI, Fig. 4). The median ciliated bands 

 have nearly disappeared, but a small trace of each of the three bands 

 reaching the mouth in the foregoing stage is still observable at the edge 

 of the body; the posterior band is still quite distinct. — The primary 

 skeletal parts have all been formed, and the teeth and the first spines 

 have appeared. Very prominent is the torus angularis, a fact the more 

 remarkable since this plate is hardly observable in the adult specimens. 

 In the two anterior radii two ventral plates are seen, one inside the other; 

 the inner one of them doubtlessly represents the first, rudimentary, inner 



1S^? n\7n''°J"; v"T^r,.^'T T'" Entwicklungsmodus der Ophiuren. (Mullers Archiv. 

 100/. p. d/U. lai. XIV. B. Fig. 1). 



