ECHINOIDEA. I. 



poison-apparatus of a ver\- peculiar aud complicated structure with sensitive cilia, poison-glands etc. 

 Only a single point seems hitherto not to have been hilly understood, viz. how the poison gland 

 opens through the large tooth at the end of each of the three valves forming the skeleton of the head 

 of the pedicellaria. Perrier") thinks that in some there is a large <lacune mediane> in the end-tooth, 

 in others he finds two terminal teeth beside each other. The latter fact is also .stated by Valentin^) 

 with regard to Sfrongyloccntroius'> lividus. SI ad en (366, p. 105) describes the end-tooth as ^channelled 

 and presenting the appearance of two or more lateral lamellae merged together to form the tip or 

 tooth-like fang . Stewart alone seems to have seen the fact correctly; he says (381, p. 910) of the 

 globiferous pedicellarise in Echinostrcplncs'. :The jaw terminates in a long, deeply grooved fang; the 

 groove, which is almost converted into a canal by the meeting of its margins, opening at a point near, 

 but never at the tip on the external or distal surface*. But this correct description seems to have 

 been overlooked. Neither seems the most recent author on this subject, v. Uexkiill, to have under- 

 stood the structure correctly, although he is not much mistaken. He sa}"s (op. cit. p. 364): <'Die Ver- 

 dickung (the upper end of the blade where the end-tooth issues) weisst jederseits eine langliche Offnung 

 auf, von der aus je ein Canal ins Innere tritt. Die beiden Canale vereinigen sich in der Mittellinie 

 zum unpaaren Giftcanal, der bis nahe an die Spitze des Endhakens lauft um hier dorsal zu miinden. 

 Der Endhaken zeigt am aussersten Ende noch eine aufgesetzte feinste Spitze . According to this 

 description v. Uexkiill seems to think that the poison-canal runs quite inside the tooth, which 

 would thus be tubular. 



An essential reason why the authors have not hitherto succeeded in reaching the correct imder- 

 standing, is no doubt that SplKPrechinus granitlaris has especially been used as the subject of exami- 

 nation, and in this species the structure of the tooth is only to be seen with some difficulty. If, on 

 the other hand, an Echinus or a Psajiuiicchiinis is used, the structure is easily seen, and when first it 

 is understood, it is also easil)' seen that the pedicellarise of SphcBr echinus are in reality constructed in 

 the same w-ay. — When the fang is viewed from above, the poison-canal is seen to be an open 

 groove on the upper surface of the fang (PI. XVII, Fig. 15), the whole reminding of the 

 poison-fangs in the opistoglypha. As mentioned by v. Uexkiill, the canal runs out a little before the 

 point; to speak of .eine aufgesetzte Spitze is misleading. (In the Cidaridaj the structure of the globi- 

 ferous pedicellarise is quite different, as described below.) 



As far as I know there is in literature next to no more exact accounts of the development of 

 the pedicellarice of the Echinoids^). Only Prouho (327) gives some excellent figures of the first 

 stages of development, but only of the histology; the development of the calcareous skeleton is not 

 mentioned. Agassiz, in the Challenger >-Echinoidea (8) PI. II, Fig. 16, gives some figures of deve- 

 lopmental stages of pedicellarise in Goniocidaris canaliciihita\ but only the outer contour is given, and 

 mention is made neither of the histology nor of the calcareous skeleton. No further direct observa- 

 tions seem to be found. — Generally, the small pedicellarise have been regarded as developmental 



1) Recherches sur les Pedicellaires et les Ambulacre.s des Asteries et des Oursins. Aun. Sc. Nat 5. Ser. XII— XIII. 1869—70. 



2) Anatomie du genre Echinus. (Agassiz: Monographies d'Echinodermes.) 1S42. 



3) On the development of the pedicellariae in Asteroidea Agassiz gives some informations. (Rev. of Echini IV.) 



