CTENOPHORA. 21 



representing nerves. Of their finer structure 1 can give no satisfactory iniorniation ; in sections they 

 are seen to be slightly sunk (PI. X, Fig. 7, the two small depressions of the epidermis at the apical 

 side; they are not quite simple depressions, but have a little elevation in the middle corresponding to 

 the fact, that there are two lines in each). 



The excretory canals and pores have been formed, viz. a single, not branching canal to 

 each side of the organ, in the sagittal plane, opening through a pore situated nearly in the median 

 line (PI. VII, P'ig. 10). On preparations of the organ in toto I have not been able to discern more than 

 one opening with certainty (PI. X, Fig. 11, excr. o.|; but sections leave no doubt of the existence of 

 both. (Comp. also PI. VII, Figs. 7—8, representing horizontal sections through the apical organ). 



The costte have now reached their highest development. They consist of 7 — 11 (or perhaps 

 a few more) iridescent combs each, the number varying somewhat; there is no difference in the sub- 

 sagittal and subtransversal costie as to the number of combs, and there is no indication of new combs 

 being added at the upper end after this stage has been reached. The combs are very long and lie so close 

 together that their number can only be made out with certainty from the cell-groups, by whicii they 

 are formed. As seen by the Fig. 7 PI. VIII, representing a vertical section through a pair of combs, 

 the^■ have the characteristic angle at the base (comp. Chun. Monogr. p. 81). The basal cells are 

 folded over the inner end of the comb, which thus proceeds from a deep ridge, this arrangement being 

 the result (or perhaps the cause) of the close aggregation of the combs, there being no room for the 

 basal cells to take the arrangement which occurs in other Ctenophores. The position of the costic in 

 deep lodges is well shown by the sections PI. IX, Figs. 6— 11 and PI. X. Figs. 2 — 6; this explains how 

 the costce in vertical sections may be seen lying apparently quite within the body (PL X, Figs. 7—9) 

 The two costa; lying in each lodge are separated by a narrow keel (PI. IX, Figs. 6 — 10). 



The tentacle apparatus is deeply sunk, enclosed by the tentacle sheath, which opens 

 through a rather long and narrow canal, directed obliquely downwards, the opening being, as stated 

 above, within the transverse furrow. The tentacles are fully developed and generally lie coiled 

 up within the tentacle sheath (PI. II, Fig.s. 8— 11, PL III, Fig. 4), the latter being then considerably 

 swollen. Sometimes, however, I have found them protruding through the sheath and penetrating 

 into the furrow, the egg-membrane not allowing it to occupy any other room. It is a simple cord, 

 covered by colloblasts, which are, however, much less numerous than in the grown specimens (comp. 

 also PL X, Figs. 2-4). The thick epithelium covering the tentacle basis has taken up its function as 

 the coUoblast-forming layer, having the same appearance as in the grown specimens (PL X, Fig. 3, 

 to compare with PL V, Figs. 1—5, PL VI, Fig. 7); at the margin this thick layer passes directly into 

 the thin wall of the tentacle-sheath (PL IX. Figs. 10 — 12). 



The transverse furrow which, as stated above, has reached so far upwards as to include 

 the opening of the tentacle .sheath, is deep and wide (PL III, Figs. 1,4; PL X, Figs. 1—9); when closed 

 as in the .specimen represented in the sections in PL X, its walls are much folded. In the middle, 

 near the mouth, the large folds, so characteristic of the grown animal, have begun to appear. The 

 epithelium of the furrow is considerably thicker than the outer epithelium (comp. the sections figured 

 on Pl.X), and has already been differentiated, the gland cells having been formed in considerable 

 number. It is distinctly ciliated. The nuclei lie mostly at the base of the cells. 



