58 



not appear to be especially numerous. The larger vascular lumina lie under the denser stratum of the connective tissue 

 (lig. 6, k', k", the great lumina) the capillaries are found close under the epithelial cells, and are in many places numerous 

 (PI. Vn, fig. 6, k). 



For the sake of comparison, I also examined the chorion fætalis of a 5V2 months gravid mare, where, as is well- 

 known, diffuse placentation occurs, and with which the Cetacean placentation has so often been compared. The chorionic 

 villi were shorter here and seemed to me to have a somewhat different character, although the ground type is the same. 

 The chorionic and subchorionic tissues were much more differentiated, being every where bundles of connective tissue: the 

 larger vessels were present in greater numbers. The chorionic villi had a flattened, simple, stratified epithelium in their more 

 peiipheral ends. No mesenchyme-like, subchorionic tissue was to be found, as in the Delphinidæ. 



In the 875 millim. long Orca foetus, the umbilical cord measured 450 millim. in length, and about 2 centim. 

 in thickness in the region a little ])elow the insertion. A little farther down, it becomes thicker and exhibits pigmentation 

 in the first 4 or 5 centim. from the insertion. It is beset with the usual small excrescences, which are also found on the 

 inside of the amnion, now more scattered, now closer together. 



The amniotic bag is very large. 



The chorion has the usual longitudinal wrinkles, and is studded with numerous villous excrescences. 



The foetal membranes at this stage of developement have probably assumed their definite form. 



Phocæiia couiuiiiiiis, Lesson. 



From my examination of the two smallest Phocæna embryos whose external form has been previously described in 

 these pages (pp. 34 — 39), I may add a few supplementary remarks on the foetal membranes in the earlier stages of developement, 

 together with a demonstration of the normal condition of the umbilical vesicle. 



I. The ovum containing the 7 millim. long embryo, was not, indeed, entire and uninjured, but it allowed 

 one to see that it was about 1 1 V2 centim. in length, of a very elongated shape, the middle portion of about 4 centim. which 

 contained the little embryo, being aljout the thickness of a little finger (1 — IV2 centim.), while the lateral portions were 

 very thin and narrow, — 2 or 3 millim. in diameter. 



The surface of the chorion was perfectly smooth, and, in the alcohol-hardened specimen, very transparent. On 

 being magnified, '}io villi were visible, hut on the other hand, a close-meshed, fine netimrJc of vessels below the surface 

 was observable. 



The allantois was elongated and band-like, but with a larger cavity than was the case in the smallest ovum of 

 Lagenorhynchus acutus. It appeared, as in that ovum, much larger in extent than the amnion. 



The amnion consisted of two concentric membranes with an intermediate space. The outer amnion, 

 amnion externum, was composed of embryonic connective tissue, and was comparatively wide and roomy. Within this was 

 a little space filled with fluid, the space being limited inwardly by the amnion internum or verum, which rather closely 

 enveloped the foetus, in the same manner as in the previously described little ovum of Lagenoi-hynchus acutus. 



The umbilical vesicle was very distinct in this ffi'tus. Seen from the abdominal surface of the foetus, especially 

 on the left side, a pear-shaped formation with a narrow stalk was observed projecting from the umbilicus (P\. IV, fig. 12 v. u.), 

 and about 0.75 or 0.90 millim. in length. The thick peripheral end was about 0.50 millim. in diameter, and the position of 

 the stalked vesicle in the umbilicus was in front, nearest the chest. The umbilical vessels are situated more caudally. 



This peculiarity of the umbilical vesicle appearing even in a very early stage of developement, like a small, almost 

 rudimentary organ, which nevei' attains to any great degree of developement, but diminishes gradually, seems to point to the 

 theory — so far as any conclusion may be drawn from the condition of the fietal membranes, — that the Cetacea, as 

 regards their phylogeny, are "old" Mammals, although, in many respects, they have retained much of a primitive Mammal type. 

 I do not hesitate in considering that the above described vesicula umbilicalis shows a perfectly normal condition by which 

 the large umbilical vesicle in the little 8 millim. long Lagenorhynchus embryo may be judged of, this latter, in my already 

 expressed opinion, having undergone an abnormal, progressive developement in size. 



II. The 17 millim. long Phocæna embryo, preserved in alcohol, was enveloped in the amnion, while the long, 

 oval chorion was open. The entire ovum had probably been about 15 centim. long. 



The surface of the chorion was wrinkled longitudinally with some small, wart-like elevations here and there in the 

 median region, which envelopes the foetus and its appendages. The peripheral portion of the chorion was quite smooth. A 

 rich, fine-meshed vascular network was seen to be stretched over the entire chorion, when magnified. 



