THE CRASPEDOTE MEDUSA OLINDIAS AND SOME OF ITS NATURAL ALLIES. 13 



cylindrical cells very similar to those of the adhesive disks of Olindioides, and the 

 secretion can be observed almost at any time, forming rounded or elongated masses 

 each corresponding to a mucus cell. The cells stain well with hematoxylin, but espe- 

 cially so near their free ends. These disks have been described as "sucking," but a 

 study of their structure reveals nothing capable of exercising a pumping action. 

 In all the known species of Gonionema these disks are situated on the inner side of 

 the tentacles, and cause the characteristic angular bend, which has given rise to the 

 generic name. 



On a cursory observation, the tentacles appear to arise from the margin of the 

 umbrella, but a closer inspection shows that they spring always from the exum- 

 brella at a short distance from the margin, just as do the exumbrellar tentacles of 

 Olindioides; and one can easily observe the endodermal tentacle roots traversing the 

 jelly to join the circular canal. In Gonionema these roots are very short, and as a 

 consequence the peronia do not come into view, although the ectoderm lying over 

 these tentacle roots is slightly thickened. 



On the inner side of the tentacles, close to the base of the velum, are the basal 

 bulbs of the tentacles, exactly corresponding both in position and number to the former. 

 These bulbs are exactly similar in structure to the rudimentary velar tentacles of 

 Olindioides, that is to say, they contain hollow prolongations of the endoderm of 

 the circular canal, and the ectoderm is clogged with developing nettle-cells. In 

 Gonionema these bulbs never become elongated and filiform, but there is no doubt that 

 they are the homologues of the velar tentacles of Olindioides. 



The marginal organs are all otocysts, and are present two at the base of each 

 tentacle. In structure they are also exactly like those of Olindioides; they are, 

 however, generally smaller, a fully developed vesicle measuring only 75 micra in 

 diameter. Again, the majority remain close to the marginal ectoderm containing the 

 outer nerve-ring, and retain a cellular connection with it; but some of the oldest 

 otocysts are pushed far into the jelly, and the cellular connection with the ectoderm 

 disappears. They remain, however, more or less closely appressed to the endoderm 

 of the circular canal (PI. Ill, Fig. 22). The otolith, when fully formed, shows a radial 

 arrangement of its constituent pyramids. 



The endodermal lamella remains one-layered throughout life, and joins the cir- 

 cular and radial canals along the line that divides the two kinds of cells as in Olindi- 

 oides. It is separated from the subumbrellar ectoderm by a thin layer of jelly. 



The coloration of the medusa is as follows: radial canals, basal bulbs, and the 

 adhesive disks of the tentacles a transparent chestnut-brown; tentacles, gonads, 

 the larger part of the manubrium, and the circular canal a lighter brown, marginal 



