53 



The external ibrm of the ovum is an elongated oval with a slight constriction in one half, which imperfectly divides 

 it into one large oval portion of -/a and one smaller more spherical portion of '/a (sec fig. 1, PI. VI). 



Some darker lines and points which shine through from within, and form dotted rows or small stars, impart a 

 certain appearance of shading to the surface, indicating the finer distribution of vessels in the chorion. The course of two 

 or three larger veins is visible on one side of the ovimi in the form of a black streak ending in the larger oval part of the 

 ovum witii a conical, black prominence: a corresponding smaller one is seen in the smaller third of the ovum. 



On cutting open the chorion and spreading it out, there is found to be a large space between the wide chorion 

 and the little amniotic bag. (See fig. 2, PI. VI). This space is filled with an exceedingly aqueous, embryonal mesenchyme, 

 which wiien magnified has the appearance of a partially transparent, greyish white, woolly mass, enveloping the amnion, 

 in the iiardened specimen, in closer layers, lining the inside of the chorion, and filling up the large intermediate space, 

 the subchorionic space. In the soft mesenciiyme of this space, the long, band-like allantois lies extended (PI. VI, 

 figs. 2 and 3, all), the shape of its broad end, which covers the amnion recalling that of a myrtle leaf. The allantois extends 

 parallel with a thick vascular cord, of which the bud-like, thickened ends can already be seen externally on the chorion, as 

 mentioned above. While the broad, leaf-shaped portion of the allantois (PI. VI, fig. 3. All) covers the amniotic bag, there 

 are visible, close to the middle of the allantois, 4 vesicle-like formations, over which it passes. These transparent vesicles 

 lie close to the amniotic bag, and are so arranged that 3 are situated on the one side, and one projects on the other side 

 (fig. 3). As figs. 2 and 3, PI. VI, show, the broad end of the allantois belongs to the larger dilated end of the ovum in 

 which the embryo lies, while the narrow end which is rounded, occupies part of the smaller spherical end of the ovum. The 

 external appearance of the allantois is speckled, a circumstance which arises from the unequal degree of transparency. Owing 

 to the preserving of the specimen, grayish, more or less transparent masses of fibrine are found precipitated upon the allantois. 

 In fig. 3 the allantois looks much narrower than it really is, because, the lumen having collapsed, it lies in folds. — From 

 about the middle, perhaps a little nearer to its broader end, goes a transverse band, which passes to the narrow, nearer end 

 of the amniotic bag. This connection of the allantois cannot, however, without the aid of magnifiers, be clearly distinguished 

 from the abundant precipitated fibrine mass. 



On raising the broad end of the allantois, the triangular amniotic bag, between 10 and 11 millim. long, could be 

 seen, and through it, the outline of the embryo was discernible (fig. 4). 



The amniotic bag (PI. VI, fig. 4, am) is of a rounded triangular shape, and envelopes very closely the little 

 foetus. The one pointed end turns towards the more isolated vesicle (fig. 4 v. u.), while the adjacent high edge of the ba" 

 is situated close to the nearest of the low of 3 vesicles. The wall of the amniotic bag is very transparent, and shows small 

 scattered, vascular ramifications. 



The vesicle-like formations (PI. VI. figs. 3 and 4) are of a varied nature. The three vesicles in a row on 

 one side of the allantois (fig. 4, b), the middle one of which lies above the other two, form enlargements full of fluid, not 

 apparently communicating with one another, l)ut closed, and adhering firmly to the chorion, one of them being probablv in 

 connection with the amnion. 



The more isolated vesicle (fig. 4, v. u.) loosened itself from its surroundings during manipulation. It measured 

 5' 2 and 6 millim. in diameter, was of an oval spheroid shape, and showed on its surface some sigmoid, grayish brown protubrances 

 (PI. VI, fig. 6). The space in which the vesicle lay proved itself to be in close connection with that place in the amniotic 

 bag whence the umbilical cord of not more than 1 or 2 millim. in length protruded. I might therefore conclude that this was 

 the vesicula umbilicalis, as it could not possibly, per exclusionem, be any other formation: otherwise it would be abnormal. 



Turner (43) makes the following statement about the umbilical vesicle: "The umbilical vesicle, again, disappears 

 in Orca some time before birth, as in the mare, pig and ruminants, and does not persist in the form of a considerable sac 

 as in carnivora, rodents, bats and insectivora; or as a rudiment, as is sometimes seen in the human subject.'" The ductus 

 omphalomesentericus (Dottergang), of which the persistence in the Phocæna until a short time before birth is pointed out 

 by Klaatsch (55), is delineated in transverse sections in various parts of the umbilical cord; but Klaatsch affirms with 

 regard to the Vesicula umbilicalis: "Von der Dotterblase habe ich bei meinen Objecten nichts gefunden." 



How far there may, in the above case of Lagenorhynchus acutus, actually be a question of a vesicula 

 umbilicalis, I am not prepared to say with perfect certainty, for, as we shall presently see, there is not a perfect guarantee 

 for it histologically, though the probability is in its favour. In this case, however, I consider it to be developed to an 

 abnormal extent; for, as we shall presently see in the case of the Phocæna, it is clearly in a very early stage of developement. 



The histological facts about the fcetal membranes in question are as follows: 



The structure of the fætal chorion tPl. VII, fig. 1). The externally smooth chorion is formed peripherally 

 of a layer of cubical epithelium (PI. VII, fig. 1, E) for the most part simple, but in a few places a double stratum, and 

 generally furnished with large nuclei. The epithelium rests upon a thin membrane of connective tissue (fig. 1, B) composed 

 of two strata of elongated, spindle-shaped and star-like cells with very few intercellular fibres. Beneath this highly 



