44 EMBEYOLOGICAL MONOGRAPHS. 



26. A later, 'balloon-sliapefl, fi-ee sta;;e as seen swimming. The positions of the mesenteries are marked liy super- 

 ficial longitudinal depressions. Eight ttutatles have already appeared. The eilia which cover tlie whole 

 body are relatively too short to be reproduced, ^f-. 



27 Ventral aspect of a young ]mra.sitic stage, showing the latero-ventral mesenterial folds, which are the first to 

 be develo[)ed. ^1^. Tlie right latero-ventral mesentery ends somewhat abruptly before reaching the aboral 

 pole. The other mesenteries are only feebly indicated in 



23. Posterior face of a cross section of the same larva 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 sec- 

 tion the depressions corresponding to the dorso-lateral mesenteries {d.-l.) are most evident, tho,se of the 

 ventral pair {v.) less distinct, and those of the dorsal pair (d.) not indicated. The ventro-laterul mesente- 

 rial folds are strongly ciliate, but cilia cannot, in the sections, be seen on other parts of the internal 

 wall. The cells uf 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. ■'-{-. 



29. A parasitic stage somewhat older tliau the preceding, stained, made transiiarcnt in clove-oil, and seen from 



the dorsal side ; magnified about 20 diameters. The edges of the ventro-lateral mesenteries ai-e seen to be 

 continuous with the ectodernuc lining of the ])haryngeal sac, and maybe 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 (?) separation between ectoderm 

 and entoderm at the oral end leaves a series of arched spaces {cam.) arouml the front end of the pharyn- 

 geal sac. 



30. Cross section through the pharyngeal sac of a stage near the preeediug. ^f. Although drawn from the ante- 



rior face of the section, tlie lithogi-apher has reversed it, so that the effect is as though it were a view of 

 the posterior face. The ectoderm is rather diagraiiiinatic, the unshaded portions being intended to repre- 

 sent the gland-cells. The row of dots at the deep surface of the ectoderm indicates diagranimatically the 

 enlargement of the basal ends of ectodermic cells. Similar rows of dots on one side of eacli 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-eetodermal layer, as at d. 



31. Anterior face of the fourth section below the free end of the pharyngeal sac, from the same individual as the 



preceding figure. \-. The ventro-lateral mesenterial filaments are cut obliquidy, 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. \-. 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 apiiroach the condilion of a taiujcnt.ial section. The middle half of the ventro- 

 lateral mesenteries, as well as the inter-mesenterial protrusions {r.nK ), are so thoroughly vacuolated as to 

 present a very porous and spongy appearance which makes tlie 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 baud takes. 

 KoTE. — On account of the small size of the drawing neither tlie 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 cycles of eight each, the 



smaller alternating regularly with the larger ; magnifieil 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 in form, the aboi'al end being 

 often much more dilated than in this figure. The mantle of amorphous matter (/3) surroumling the column 

 is the product of ectodermic secretions, and forms a loose tube witliin which the auiiiial may retire. 



34. Edwardsia? From C. Claus, Bcnierkungen iiber Ctenophoren und Medusen. Zeitschr. f. wiss. Zool., r>d. 



XIV. Taf. XXXVIl. fig. 7. A spheroidal larva from Messina magnified about 20 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 idoar homogeneous .substance. Two of the twelve (S?) meridional rows of large 

 orauge-yellow fat-globules are indicated by rfll. ol. There are four coiled tciita.de-like arms (na'.scntcrinl 

 filaiiients '() wliiidi may be protruded through the mouth oiieuiug. 



NoTiC— It is probable from the statements of the bruthers Hertwig {np. cil. jip. 12l!, 127) that this is 

 the young either of an Edwardsia or a nearly related unknown form, since it has four jiairs of mesenteries 

 with well developed muscular bauds, which have exactly tlu' same arrangement around the pharvngcal 

 sac as in Eduxirdsia. 



