Structure of Mage\ona. 455 



action of the water laterally, and presents in the fresh 

 animal the aspect of a granular area crossed by numerous 

 convolutions or folds, which often change their appearance 

 under examination, like those formed in a translucent and 

 very fine chitinous membrane. The whole, indeed, simulates 

 a convoluted duct most closely, since the folds retain a 

 uniform size throughout, though they are liner at one end of 

 the mass. The latter can with care be enucleated from its 

 covering, but in those examined no clear evidence of well- 

 formed ducts (e.ff. indication of a central cavity or an entirely 

 free coil, on tearing) could be observed. It is possible that 

 the ambiguous structure was only partially developed and 

 that the folds may afterwards attain further differentiation. 

 The exact function of this structure is unknown, and its 

 presence in both sexes would show that it is not indispensably 

 related to the ova. It appears to be homologous with the 

 external ovaries or egg-racemes described by Prof. Mobius in 

 Leipoceras uviferum, a form which closely resembles Po///^/ora*. 

 It is still more nearly related to the egg-sacs (resembling a 

 swallow's nest) mentioned by the same author as present 

 along the sides of Scolecolepis cirrata, Sars f. It may be 

 that the folded structure in Mmjelona acts the part of the 

 network in Scolecolepis^ by which the eggs are held in the 

 pouches, but no proof of this has yet been observed. The 

 whole arrangement, however, seems to be much more largely 

 developed in Mayelona. The analogy of this structure with 

 a segmental organ can only be conjectural, though it is 

 suggestive that M. Claparede describes a similar but more 

 highly differentiated organ within the posterior region of the 

 body in Chcetopterus. Finally, so little is known of the life- 

 history of Ma^e/o/m, that nothing can be said of its connection 

 with sexual or other variations. 



No opportunity, unfortunately, was available for investi- 

 gating the development of the species at St. Andrews. 

 Though mature animals were abundant in summer, the 

 extreme heat prevented success in this respect in the confined 

 vessels, especially after the long journey from the sea-coast, 

 while those with the reproductive elements developed late in 

 autumn failed to afford a single embryo |. As previously 

 indicated, M. Claparede found a developing form which he 



* Ann. & Mag. Nat. Hist. 4tli ser. vol. xiii. p. 201. 



t Op. cit. p. 260. 



X The surface of the sea was examined by the towing-net from the 

 margin of full tide outward for several miles in September, but no larval 

 type connected with this form was obtained. In subsequent years, how- 

 ever, all stages have been procured at St. Andrews. 



