42 MRS. LEONORA J. WILSMORE ON SOMlfi 



enclosing a very large lumen. A single row of nematocysts of varying sizes 

 is placed on the outer border of the ectoderm, more sparsely than in the column- 

 wall. They are of two kinds, one only of which takes the hsematoxylin 

 stain. The nucleated zone is very deep, and the clear nervous zone is 

 penetrated by numerous plaitings of the mesoglcea, which carry a strong 

 ectodermal muscle. The mesoglcea and endoderm are thin. The histology 

 of the disc resembles that of the tentacles, but a slight endodermal muscle is 

 also present. 



(Esophagus (PL 4. figs, o & 4). — The most striking feature of the oesophagus 

 is the single enormous siphonoglyphe (PI. 4. figs. 3 & 4, and text-figure A). 

 This large firm structure extends from the mouth to a point in the body- 

 cavity some distance below the rest of the oesophagus. Its total length 

 in the adult specimen is 1*6 mm., and it terminates 3'7 mm. fi'oni the 

 posterior end of the body. 



The ventral directives (PI. 4. figs. 3 & 7, 3 3, and text-figure A, 3 3), by 

 which alone it is supported throughout, remain attached to it below the 

 oesophagus, where it hangs freely in the body-cavity. In fig. 3 a dotted line 

 shows the internal boundary of the siphonoglyphe. In the adult specimen 

 it remains an open tube throughout and its walls enclose a space almost equal 

 in area to the rest of the oesophagus. In the larval form the two endoderm 

 walls are approximated fit the entrance to the oesophagus during part of their 

 length, and the siphonoglyphe encloses a relatively smaller area than in the 

 adult. 



The ectoderm is deeply folded and of equal thickness in both oeso})hagus 

 and siphonoglyphe, but becomes thicker in the lower part of the siphono- 

 glyphe. It contains many long gland-cells, especially numerous in the 

 siphonoglyphe, and a row of fine small nematocysts lies in its outer border, 

 while the nucleated layer is very deep. The mesoglcea is finely laminated in 

 the adult ; but in the larval form the laminse are very loose, and show also 

 many light circular patches. The mesoglcea of the oesophagus proper is very 

 thin ; that of the siphonoglyphe extremely thick and stiff, but this thickness 

 decreases somewhat in the lower part. The endoderm, which is thicker in 

 the siphonoglyphe than elsewhere, is not sufficiently well-preserved for 

 description. 



Mesenteries (PI. 4. figs. 3, 7, 8, and text-figure A). — There are in the adult 

 form twelve perfect and eight imperfect mesenteries. The latter consist of 

 four very small pairs situated in the lateral and sulcar exocoeles (PI. 4. 

 figs. 3, 7, and text-figure A). Although no gonads are present the coelen- 

 teron on dissection was found almost completely filled with a solid mass 

 formed of the perfect mesenteries. This is markedly the case in the upper 

 sub-oesophageal region, where the digestive endoderm is very thick and 

 divides into several branches each provided with a mesenterial filament. 

 Four pairs of the mesenteries, viz. 1 1, 2 2, 3 3, and 4 4, are attached to 



