28 DISCOPHOR^. Part III. 



to constitute the -whole outer wall, sho^ving the remarkable compressibility of the 

 original cells, among which the lasso-cells are imbedded. 



At this age it may be seen that tlie hydroid form of covered-eyed Medusae 

 has a horny tube (PI. X". Fi(js. 4 / and 4^ /), as well developed as any Hydroid 

 of the naked-eyed families. Neither Coryne nor Tubularia can be said to liave more 

 fully develoijed horny tubes than this; nor is there any gejius out of the families 

 of covered-eyed Medusce which have so thick-walled a tube. The inner surface 

 of this tube (/) presses very closely to the stem {Fig. 4* a) of the embryo, but 

 does not touch it. i^t its lower end it spreads out into a broad base, and directly 

 under the foot (c^) of the pedicel (« h) it is -connected with it by several — four 

 to seven or eight — small, slender, conical props (/') ; passing upwards, it thins out 

 into a mere film (/"), and finally comes to an edge at a short distance above 

 the bottom of the cup-shaped head. At first sight, owing to the longitudinal 

 wrinkling of the surface, it would ajipear to be composed of concentric layers, but, 

 on account of its exceeding transparency, no such structure can be discovered; 

 although, considering that such sheaths are formed by successive deposits, there is 

 no doubt that the layers are present. In color the tube resembles amber, and, 

 like that substance, it changes its intensity of coloring accoi-ding to the light which 

 shines through it. We have not seen a horny sheath around the stem of the 

 scyphostoma of Aurelia, nor has it been observed by European naturahsts in this 

 genus.^ 



This is the earliest period at which we have observed the embryo taking food. 

 The first instance of this which we saw was a six-armed individual (PI. X. Fir/. 30), 

 which had in its digestive cavity one of its own kind, in the j^hinula state, and 

 revolving by means of its own cilia at a very rapid rate. The jDlanula continued 

 to revolve for three quarters of an hour after we first saw it, and then, being 

 ejected, it swam away. In Fig. 35 we have an embryo in the act of casting 

 out the rejectamenta of its food with the help of one of its tentacles. 



It frequently happens that an embrj'O is altogether destitute of a horny sheath, 

 and may be seen moving from place to place by walking on its tentacles. Often- 

 times we have seen one of them seated upon the top of another embryo, either on 

 the edge of the upper disk or nearer the mouth; and, in some instances, the base 

 (PL X*. Fig. 12 c^) Avas embraced by the lips (e) of the lower individual. In the 

 latter instance it was always very difficult to determine that the two embryos were 



^ The absence of the horny sheath in Sars's of Aurelia. According to Dr. "Wright (Edinburgh 



figures (Wieginanu's Arehiv, 1841, Band 1, PI. I. New Phil. Journ. 1859, vol. X. p. 106, PI. VIII. 



Figs. 25-42), leads us to assume, what he is in Fig. 2), the scyphostoma of Chrysaora has a ''gela- 



doubt about, that they represent the scyphostoma tiuous case, corallum, or polypidom." 



