54 



cellular tissue is a jelly-like mesenchyme with few cells (tig. 1, M) strongly recalling the mesenchyme in Ccelenterata. The 

 peripheral part of the mesenchyme is distinguished by its sparse, wavy fibres (fig. 1, M). which run in one special direction, 

 while the scattered cells are of the nature of large wandering cells, with here and there an indication of a star-like shape, 

 or with pseudopod-like off-shoots. The transverse section of capillary vessels, with here and there a larger vessel, is also 

 found. — In the deeper-lying parts, the coloured specimens present a more granular appearance, and small, oblong vacuoles 

 ('fig. 1 V c) while the fibrous element is less prominent. 



Seen from the surface, the chorion exhibits a large-meshed network of vessels (PI. VI, fig. .5) under the epithelium 

 in the peripheral layer of connective tissue; in section, these appear only as scattered vessels forming a large-meshed 

 capillary network. 



The structure of the amnion exhibits a simple, flattened epithelium, witli a thin embryonic connective tissue 

 outside, in wliich small scattered vessels and capillaries are seen. The amnion is divided by a distinct fissure from the 

 surrounding mesenchyme. 



The structure of the allantois (PI. VII, fig. 2). A piece of the band-like allantois was cut off, coloured and 

 microtomised. The transverse sections show an inner, fissure-like cavity, the cavity of the allantoic bag (fig. 2, al). This 

 is lined inside with a simple stratum of flattened epithelium (fig. 2, a e), wliich rests upon a peculiarly-formed foundation of 

 connective tissue (fig. 2, a b). On first glancing at the carmine-coloured specimens, one is reminded of prismatic or high 

 cylinder epithelial cells. The flattened epithelium is in most places loosened from the connective tissue, and lies in elongated, 

 coherent strata in the lumen of the allantoic sac, in some places rolled together into masses, and in others lying close up to 

 the connective tissue. This tissue is comparatively thick, and is distinguished by a closer intercellular substance that is more 

 readily coloured in carmine, and which lies next the epithehum. It is of the nature of an embryonic mucous tissue, with 

 variously shaped cells, now spindle-shaped, now polygonal, and its off-shoots lying in a ground substance which readily 

 becomes coloured. The peripheral cellular layer consists of elongated, mostly spindle-shaped cells (fig. 2, a d). The intercellular 

 substance is homogeneous, as it is only in the peripheral layer that there are here and there fibres of connective tissue. In 

 a few places, there are little clusters of proliferative embryonic tissue cells. Klaatsch's description of high cylinder cells 

 in the allantois in Phocæna, I am quite unable to substantiate in Lagenorhynchus acutus. 



The allantoic lumen is everywhere very small, in many places only like a narrow fissure, which indicates that there 

 must have been only a very little allantoic fluid. 



The supposed umbilical vesicle (PI. VI, fig. 6) was coloured and microtomised. The sections showed that the chief bulk 

 of the walls consisted of embryonal connective tissue, while a simple, flattened epithelium was with difficulty seen upon the inside. 

 The thickenings in the wall, which were easily seen with the naked eye, consisted, histologically, for the most part of embryonic 

 connective tissue, which seemed to be in a very proliferative condition (PI. VII, fig. 4) — little intercellular substance, and 

 many cells which were very chromophilous. In one of the thickenings of the wall are constantly seen one large, or 2, 

 sometimes 3 smaller lumina (fig. 4, o.nn, lined with a beautiful cylindrical epithelium; in the large lumen this is cubical 

 (PI. VII, fig. 4. ep), in the small ones high cylindrical. These epithelium-lined lumina greatly resemble a large glandular 

 duct. If my explanation of the hollow vesicle is correct, I must consider the large lumen as belonging to the ductus 

 omphalo-mesen teriens, and the small lumina as belonging to abnormally developed ramifications of the same. There are, 

 moreover, in many places on the walls of the vesicle, large and small thickenings, of which the many chromophilous, close- 

 lying cells point to a probably abnormally energetic growth in this embryonal organ. In a few sections, where the thickening 

 includes a longer portion of the wall, may be seen 2 close-lying vascular lumina and 2 epithelium-lined lumina. 



On making a section through the entire amniotic bag with the adjacent three vesicle-like formations and the 

 allantois, my supposition that the vesicles lying side by side must be enlargements of the amniotic bag, was strengthened, 

 thiiuiih not in its entirety; for I could not with certainty prove the presence of epithelium on the inside. Only one of them 

 seemed to consist of a thin epithelium, and must therefore belong to the amnion. The two other vesicles, however, I consider 

 as abnormally-shaped enlargements in the mesenchyme lying nearest to the outside of the amnion. None of these vesicle 

 Ibrmations were to be found in the fcetal membranes of the small Phocæna embryo subsequently examined, nor had the well- 

 developed amnion in that specimen a small, shrivelled lumen, ])ut on the contrary, a large one. Both ova, however, agree 

 in the circumstance that the allantois is well developed at a very early stage, and is of comparatively large dimensions. 



Upon the whole, the impression obtained from this ovum containing the 8 millim. long embryo, was that of an 

 abnormal developement, abnormal at any rate in certain directions, although in other respects it is normal. 



Recapitulation. The 7.5 millim. long, oval ovum, containing the 8 millim. long embryo, presents a smooth 

 chorion with several longitudinal folds, and only indications of incipient villi in a few places. The subchorionic space is 

 probably abnormally large, being filled with a richly succulent mesenchyme. The ribbon-like allantois, from 35 to 40 

 millim. in length, has a broad, leaf-like dilated end, where the embryo lies, and shows a simple, flattened epithelium, which 

 liniis tlie lumen. The amniotic bag is 10 millim. in length, triangular in form — probably oval in the fresh specimen — 



