ECHINOIDEA. I. 



poison-apparatus of a very peculiar and complicated structnre with sensitive ciiia, poison-glands etc. 

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

 opens through the large tooth at the end of each of the three valves fomiing 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 faet is also stated by Val en tin 2) 

 with regard \.o Strongyloccntrotiis> lividas. SI ad en {366, p. 105) describes the end-tooth as channelled 

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

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

 globiferous pedicellariæ in Echinostrcphus: The jaw terminales 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 structnre correctly, although he is not much mistaken. He says (op. cit. p. 364): Die Ver- 

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

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

 zuni unpaaren Giftcanal, der bis nahe an die Spitze des Endhakens låuft nm hier dorsal zu miinden. 

 Der Endhaken zeigt am åussersten 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 tubnlar. 



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

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

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

 the other hånd, an Echimis or a Psaininechinus is used, the structnre is easily seen, and when first it 

 is understood, it is also easily seen that the pedicellariæ of Sphærcchinus are in reality constructed in 

 the same way. — When the fang is viewed from above, the poison-canal is seen to be an op en 

 groove on the upper sur face of the fang (PI. XVII, Pig. 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 aiifgesetzte Spitze is misleading. (In the Cidaridæ the structiire of the globi- 

 ferous pedicellariæ is quite different, as described below.) 



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

 the pedicellariæ of the Echinoidss). 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 »-Ecliinoidea (8) PI. II, Fig. 16, gives some figures of deve- 

 lopmental stages of pedicellariæ in Goniocidaris canaliciilata\ 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 pedicellariæ have been regarded as developmental 



I) Recherches sur les Pédicellaires et les .\mbulacres des Astéries et des Oursins. Aun. Se. Nat. 5. Sér. XII— XIII. 1869 — 70. 



=) Anatomie du genre Echinus. (Agassiz: Monographies d'Echinodemies.) 1842. 



3) On the development of the pedicellariæ in .\steroidea Agassiz gives some informations. (Rev. of Echini IV.) 



