110 Mr. W. Percy Sladen on the 



goes, by SpJicerechinus granulans. But from a study of the 

 development of the sacculiferous pedicellarice globiferoz of this 

 species and of the structure of the ordinary form of ped. glo- 

 hifera in other Echini, I am inclined to consider that this 

 is perhaps not so abnormal after all, and that the occurrence 

 may be explained by derivation and advanced development. 



Hitherto the ped. globiferai of Echini have been simply 

 described as possessing a globose fleshy head attached imme- 

 diately to the calcareous shaft of the stem, both head and 

 stem being alike covered with a common investing membrane. 

 No mention has been made of the detail of the special ana- 

 tomy of these parts. 



The pedicellaria globifera of Echinus melo may be taken 

 as a typical form for our present purpose. The superficial 

 differences which at once strike the attention are the com- 

 paratively smaller size, the presence of two external and visi- 

 ble sacculi on the outer portion of each valve of the head, the 

 gradual widening or expansion of the investing membrane of 

 the stem immediately under the head, and the absence of any 

 trace of sacculi on the stem. 



A longitudinal section of this pedicellaria shows the gland- 

 bearing sac of the valve, its muscular investment, the tactile 

 cushion, the powerful muscles of the valves, and the attach- 

 ment upon the distal extremity of the stem-rod. Each of 

 these parts is referable to a similar structure already enu- 

 merated when treating of the section of the pedicellaria of 

 Sphwrechinus granulans ; and for the present purpose it will 

 not be necessary to indicate the special modifications they 

 present in this form. The expanded portion of the investing 

 membrane of the pedicellaria immediately underneath the 

 head in E. melo demands, however, especial attention. 



"Within this expansion there is seen to occur immediately 

 below the gland-sac of the valve an irregular, more or less 

 coarsely cellular cavity or space, which is filled with mucous 

 matter (PI. XIII. fig. 13, x), and from which there appears to 

 be an opening leading on to the inner surface of the calca- 

 reous axis of the valve-frame, by which means the mucus is 

 probably conducted on to the under (?) side of the fang 

 (PI. XIII. fig. 13). I am unable to state positively at present 

 whether the mucus is secreted originally within this chamber 

 or not ; for although a few large cells with long connective 

 fibres may be seen within the mucous mass of the cavity, I 

 cannot say whether they are gland-cells or not ; and the doubt 

 is also further increased by indications of what may probably 

 turn out to be an opening between the gland-sac of the valve 

 and the cavity in question. However this may be, there 



