INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 653 



The manubrium is large ; it commences with a quadrate base, and 

 when extended projects beyond tlie margin of the umbrella. The 

 mouth is destitute of tentacles, but is divided into four lips, which 

 are everted and plicated. The endoderm of the manubrium is thrown 

 into four strongly-marked longitudinal plicated ridges. 



The radial canals are four in niunber ; they originate each in an 

 angle of the quadrate base of the manubrium, and open distally into 

 a wide cii'cular canal. Each radial canal is accompanied by longi- 

 tudinal muscular fibres, which spread out on each side at the junction 

 of the radial with the circular canal. 



The velum is of moderate width, and the extreme margin of the 

 umbrella is thickened and festooned, and loaded with brownish-yellow 

 pigment-cells. 



The attachment of the tentacles is peculiar. Instead of being free 

 contrnuations of the umbrella margin, they are given off from the 

 outer surface of the umbrella at points a little above the margin. 

 From each of these points, however, a ridge may be traced centri- 

 fugally as far as the thickened umbrella margin ; this is caused by 

 the proximate portion of the tentacle being here adnate to the outer 

 surface of the umbrella. It holds exactly the position of the " Man- 

 telspangen " or peronia, so well developed in the whole of the 

 NarcomedusaB of Haeckel, and occurring also in some genera of his 

 Trachomedusae. Its structure, however, diifers from that of the true 

 peronia, which are merely lines of thread-cells marking the path 

 travelled over by the tentacle, as the insertion of this moved in the 

 course of metamorphosis from the margin of the umbrella to a point 

 at some distance above it, while in Limnocodium the ridges are direct 

 continuations of the tentacles wliose structure they retain. They 

 become uaiTower as they approach the margin. The number of the 

 tentacles is very large in adult specimens. The four tentacles which 

 correspond to the directions of the four radial canals or the perradial 

 tentacles are the longest and thickest. The quadrant which intervenes 

 between every two of these carries, at nearly the same height above 

 the margin, about thirteen shorter and thinner tentacles, while 

 between every two of these three to five much smaller tentacles are 

 given ofi" from points nearer to the margin, and at two or three levels, 

 but without any absolute regularity ; indeed, in the older examples 

 all regularity, except in the primary or perradial tentacles, seems 

 lost, and the law of their sequence ceases to be apparent. 



No indication of a cavity could bo found in the tentacles ; but 

 they do not present the peculiar cylindrical chorda-like endodcrmal 

 axis formed by a series of large, clear, thick-wallod cells which is so 

 characteristic of the solid tentacles in the Trachomedusrc and Narco- 

 mcdusa). From tlie solid tentacles of these orders they ditfer also 

 in their great extensibility, the four perradial tentacles admitting of 

 extension in the form of long, greatly attenuated filaments to many 

 times the height of tlie vertical axis of the umbrella, even when this 

 height is at its maxiumm ; and being again cajjablo of assuming by 

 contraction the form of short thick clubs. Indeed, instead of pre- 

 r,((nting the Cdiuparatively rigid ami imperfectly contractih; character 



