44 EMBRYOLOGICAL MONOGRAPHS. 
26. A later, balloon-shaped, free stage as seen swimming. The positions of the mesenteries are marked hy super- 
ficial longitudinal depressions. Eight tentacles have already appeared. The cilia which cover the whole 
body are relatively too short to be reproduced. 12. 
27. Ventral aspect of a young parasitic stage, showing the latero-ventral mesenterial folds, which are the first to 
be developed.72. The right latero-ventral mesentery ends somewhat abruptly before reaching the aboral 
pole. The other mesenteries are only feebly indicated in 
28. Posterior face of a cross section of the same larya near the middle of the anterior half (a, fig. 27). De- 
pressions in the surface of the entoderm show the places where the mesenteries will appear. In this see- 
tion the depressions corresponding to the dorso-lateral mesenteries (d.-/.) are most evident, those of the 
ventral pair (v.) less distinct, and those of the dorsal pair (d.) not indicated. The ventro-lateval mesente- 
rial folds are strongly ciliate, but cilia cannot, in the sections, be seen on other parts of the internal 
wall. The cells of these folds are wedge-shaped-columnar in form, whereas all the rest of the inner 
cell-layer is of a spongy or reticulated appearance and the cell boundaries are not distinguishable. 44% 
29, A parasitic stage somewhat older than the preceding, stained, made transparent in clove-oil, and seen from 
the dorsal side ; magnified about 20 diameters. The edges of the ventro-lateral mesenteries are seen to be 
continuous with the ectodermice lining of the pharyngeal sac, and may be traced to the middle of the poste- 
rior half of the body, where they appear in the drawing to meet by convergence. The ectoderm is thick at 
both ends, but much thiuner along the sides of the larva. An artificial (7) separation between ectoderm 
and entoderm at the oral end leaves a series of arched spaces (cam.) around the front end of the pharyn- 
geal sac. 
30. Cross section through the pharyngeal sac of a stage near the preceding. 72. Although drawn from the ante- 
rior face of the section, the lithographer has reversed it, so that the effect is as though it were a view of 
the posterior face. The ectoderm is rather diagrammatic, the unshaded portions being intended to repre- 
sent the gland-cells. The row of dots at the deep surface of the ectoderm indicates diagrammatically the 
enlargement of the basal ends of ectodermic cells. Similar rows of dots on one side of each of the mesen- 
teries represent the cut ends of the longitudinal muscles of the mesenteries and are somewhat too strongly 
marked. The muscles are only feebly developed at this stage. Spindle-shaped nucleated cellular ele- 
ments are scantily present in the homogeneous sub-ectodermal layer, as at eZ. 
31. Anterior face of the fourth section below the free end of the pharyngeal sac, from the same individual as the 
preceding figure. 72. The ventro-lateral mesenterial filaments are cut obliquely, especially the one of the 
left side. The vacuolated nature of the entoderm is particularly noticeable when it projects, as is often 
the case, in thick longitudinal ridges into the common cavity of the body. These thickenings (en/.), al- 
though constantly occurring in all the interspaces between mesenteries, are very irregular in their dimen- 
sions. Compare figure 33, where, as is always the case with later stages, they are more conspicuous than 
the mesenteries themselves. : 
32. Anterior face of a cross section near the aboral end, from another specimen of about the same age as the preced- 
ing. 42. The entodermic ingrowths nearly fill the digestive space, and have a peculiar zig-zag course, not 
well reproduced by the lithographer. This peculiar appearance results from the fact that the section is so 
near the aboral end as to approach the condition of a tangential section. The middle half of the ventro- 
lateral mesenteries, as well as the inter-mesenterial protrusions (e7!.), are so thoroughly vacuolated as to 
present a very porous and spongy appearance which makes the histological distinction between the thickened 
free margins of these mesenteries (the mesenterial filaments) and the more peripheral parts of the mesen- 
teric folds very conspicuous. This difference is intensified by the deep stain which the marginal band takes. 
Nore.—On account of the small size of the drawing neither the vacuolation nor the structure of the 
mesenterial bands have been well reproduced by the lithographer. 
33. Ventral aspect of a living specimen possessing sixteen tentacles arranged in two eycles of eight each, the 
smalier alternating regularly with the larger; magnified about 7 diameters. The transparency of the ani- 
mal allows one to see the short pharyngeal sac and the mesenteries of the opposite wall, although, to avoid 
confusion, the latter have not been drawn. The animal is very changeable iu form, the aboral end being 
often much more dilated than in this figure. The mantle of amorphous matter (8) surrounding the column 
is the product of ectodermic secretions, and forms a loose tube within which the animal may retire. 
34. Edwardsia? YVrom C. Claus, Benerkungen iiber Ctenophoren und Medusen. Zeitschr. f. wiss. Zool., Bd. 
XIV. Taf. XXXVII. fig. 7. A spheroidal Jarva from Messina magnified about 25 diameters. The walls 
consist of a small-celled ciliated entoderm and an ectoderm of large cells, the two cell-layers being separated 
by an intervening layer of clear homogeneous substance. Twwo of the twelve (8?) meridional rows of large 
orange-yellow tat-globules are indicated by gt. ol. There are four coiled tentacle-like arms (mesenterial 
filaments ?) which may be protruded through the mouth opening. 
Norr.— It is probable from the statements of the brothers Hertwig (op. cit. pp. 126, 127) that this is 
the young either of an Ldwardsia or a nearly related unknown form, since it has four pairs of mesenteries 
with well developed muscular bands, which have exactly the same arrangement around the pharyngeal 
sac as in Ldwardsia. 
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