22 DISCOPHOR^. Part III. 



converted into a wdl, but portions of it, sometimes to a considerable amount, are 

 torn away from the principal mass and cast out from the body, as if the residue 

 of digestion. The first discharges from the intestines of the higher animals no 

 doubt correspond to the waste matter of this young animal. 



The horny sheath does not appear at any precise time, but varies considerably 

 in this respect, as we may see in the next phase which we have to illustrate 

 {Figs. 13 and 13") ; here the tentacles (e) are quite prominent, and yet there is 

 not the least trace of a sheath to be observed. The digestive cavity is quite 

 small, even less than in the last stage, and the opaque orange mass darkens the 

 whole body to the very base of the tentacles. The cilia are still present, but 

 immovable. In the next phase we may see that the tentacles {Figs. 14, 14% and 

 14^ e) develope very early their characteristic organs, the lasso-cells (PI. X". Figs. 7 

 a h and 10), and in such abundance that the parietes of the outer wall appear to 

 be entirely composed of them. The outer wall (PI. X. Fig. 14 a) of the body is 

 very thin, and is composed of a single layer of cells, excepting in the tentacles, 

 where the lasso-cells constitute a single layer by themselves, and the interior of the 

 wall {Fig. 14 «^), which here is very thick, is composed of an irregular mass of 

 cells, identical with those of the rest of the body (PI. X^ Fig. 8). There are also 

 lasso-cells scattered all over the body. The tentacles (PI. X. Fig. 14 e), as far as 

 they project beyond the general surface of the body, are almost entirely made up of 

 a thickening of the outer wall {Fig. 14 a)-), the inner wall forming as yet only 

 a short basal portion. The tentacles are so exceedingly contractile that it is next 

 to impossible to determine whether aU four of them are of equal age, or any one 

 or two older than the others. In the figure which we have given representing 

 the animal as seen from above {Fig. 14''), the two longer tentacles would seem 

 to be much older than the others; but when we see them at the next moment 

 all retracted, and so merged into the walls of the body that the embryo appears 

 like a perfectly smooth cup {Fig. 14°), without the least trace of any appendages, 

 it becomes clear, that, at this age, size has nothing to do with the degree of 

 development at which the young has arrived. It is hardly conceivable that the 

 simple, cup-like body with its widely-gaping mouth {Fig. 14° c) and perfectly smooth 

 exterior is the same individual that a moment before bore such prominent tentacles 

 {Figs. 14, 14% and 14'' e) ; and yet we have watched the transition from one state 

 to the other without removing the eye from the microscope. The inner wall {h) 

 is very thick and opaque; its interior surface is smooth and Avell defined, so that 

 we may consider the digestive cavity {d) as firmly established and ready to per- 

 form its characteristic function. Taking advantage of the enormous gaping of the 

 mouth, we have been able to study the cells of the interior surface of the inner 

 wall {Fig. 14° d), and find them (PI. X^ Fig. 8) to be identical with those of the 



