ON THE DEVELOPMENT OF SOME BRITISH ECHINODEIIMS. 15 



ferred to S-patangus purpureus did really belong to that species. It was 

 therefore very satisfactory to me to get the opportunity of rearing the 

 larva of this species during my stay in Plymouth. It proved to be very 

 easy to rear ; the larvae developed normally and reached their full size 

 in the course of three weeks. The fertilization was made on the 23rd 

 June ; on the 14tli July the larvge had all their processes developed, and 

 the first sign of the metamorphosis (formation of the oral disc) had 

 appeared. Unfortunately I cannot utilize this culture for a complete 

 description of the larval skeleton, on account of the mishap explained 

 above. Still some notes can be given which may prove sufficient for 

 the certain recognition of the larva. 



The shape of the fully formed larva is, as shown in Figure 14, that of 

 the typical Spatangoid larva. It is especially to be noticed that the 

 postero-lateral processes are long and slender (and a little posteriorly 

 directed) as in other Spatangoid larvae, not short, broad, and rounded as 

 stated by Krohn. If it is, upon the whole, really the S. purpureus larva 

 which Krohn has observed, it must then have been in a stage where the 

 postero-lateral processes are just about to appear. According to his 

 description, " Beobachtungen iiber Echinod. larven," p. 209, quoted in 

 Echinodermenlarven der Plmikton Expeditio7i, the body shape of the larva 

 is rather compbcated, with lobes and folds ; in reality it is quite simple, 

 without folds, as seen in the figure. It is, then, most probable that the 

 larva described here by Krohn is not at all the aS. purpureus larva, but 

 the larva of another jMediterranean Spatangoid — ^which species cannot be 

 ascertained at present. The only thing in the description of Krohn 

 which agrees with the S. purpureus larva is the extraordinary length of the 

 postoral, postero-dorsal, and, especially, the posterior processes. Very 

 probably also the other processes will attain a greater length than shown 

 in the figure. They are a little swollen at the point, which is conspicu- 

 ously coloured with red pigment. A feature to be noticed about the 

 larva is a groove inside the posterior transverse chord (Fig. 14) ; the mean- 

 ing of this groove is unknown to me. 



The skeleton is, as shown by Krohn, characterized by the fact that the 

 fenestrated rods (postoral, postero-dorsal, and posterior) have no holes 

 in their basal part ; in the posterior rod it is, however, only quite a short 

 part which is unfenestrated (Fig. 15), in the other rods the unfenestrated 

 part may really be as long as figured by Krohn (" Uber die Larve von 

 Spatangus purpureus,'' Taf. VII, 2-3) ; characteristic also is the widened 

 basal part of the antero-lateral rods (cf. Krohn, Taf. VII, 5). The most 

 important point to settle in regard to the skeleton is the structure of the 



