Pedicellaria in the Echinidae. 113 



for the capture of passing organisms for the purpose of food, 

 or even for their retention until decomposition has set in and 

 the accompanying crowds of infusoria have been produced, 

 seems to me highly improbable when we take into account 

 the character and behaviour of the pedicellarise themselves 

 and the constantly moving currents of water which the envi- 

 ronment of the sea-urchin naturally presupposes, irrespective 

 of any consideration as to the kind of food required by the 

 animal. Besides this, if it were the case that these pedicel- 

 larige were put to such a use, the jaws or head-valves would 

 frequently be found filled with decaying matter — a circum- 

 stance which, so far as my own observations go, very seldom, 

 if ever, happens. 



EXPLANATION OF THE PLATES. 



Plate XII. 



Fig. 1. Pedicellaria globifera of Sph&rechinus granulans. The valves of 

 the head nearly closed. The glandular dilatation on the stem 

 is somewhat distended ; and one of the sacculi is seen disrupted 

 by the action of very dilute spirit. X 18. 



Fig. 2. Head of another example of the same form of pedicellaria, placed 

 slightly obliquely to show the under portion. The valves are 

 closed; and their sacculi are more ample towards the extremities 

 than in the previous figure. X 13. 



Fig. 3. The same form of pedicellaria with the valves of the head ex- 

 panded. A portion of the investing membrane of the stem- 

 dilatation has been cut away ; and the internal glandular body 

 of one of the sacculi is seen displaced. X 13. 



Fig. 4. Another example in which a portion of the investing membrane 

 has been removed, in order to show the glandular body in situ. 

 The head is represented in outline, and the position of the in- 

 ternal calcareous skeleton of the valve is indicated. X 13. 



Fig. 5. The same form of pedicellaria, expanded as in figs. 3 and 4, and 

 seen from above, showing the position of the tactile cushions. 

 X 13. 



Fig. 6. The stem of a pedicellaria globifera in which the stem-sacculi 

 are wanting, the foramina only being present, x 13. 



Fig. 7. Immature stage of pedicellaria globifera from a young specimen 

 of Sphcerechinus granulans. X 24. 



Fig. 8. Transverse section through one of the sacculi of the stem of pedi- 

 cellaria globifera : X 470. a, epithelium ; b, neuro-muscular 

 layer ; c, cellular layer ; d, gland-cells and ducts ; e, mucous 

 mass. 



Plate XHI. 



Fig. 9. Longitudinal section through the head of the ped. globifera of 

 S. granulans, cut slightly oblique: X 57. a, ephithelium; 



b, thin layer of connective tissue with isolated nerve-cells ; 



c, muscular wall of the sacculus ; d, gland-cells ; e, muscles of 

 the valves ; /, muscles in connexion with the tactile cushion j 

 g, the tactile cushion. 



