THE SYSTEMATIC ANATOMY OF A FCETAL SEA-LEOPARD. 243 



numbers of fetal capillaries, whilst maternal vessels of rather wider 

 calibre lie in the mesodermic septa and become at times surrounded by 

 portions of the syncytium. 



(c) A zone in which an invasion of the superficial gland-layer of the uterine 



mucosa has taken place, the syncytium of the villi having at an earlier 

 phase converted the uterine epithelium into what Grosser terms a " sym- 

 plasma," and becoming as it were welded with the mucosa at numerous 

 points ; the partitions between the glands become also fixed to other 

 villous tufts. 



(d) A deeper layer which comprises the bases of the uterine glands, and lies 



next the uterine muscle. The muscular coat, which is in the present case 

 thin, contains large branches of the maternal blood-vessels, and these, 

 where the interglandular septa pass to become fixed to the syncytium 

 of the villi, pass into the mesoderm lying between the lamellae of 

 the placental labyrinth. 



It appears that zone c noted above (so-called " umlagerungszone " of Strahl and 

 Grosser) is, during the earlier phases, of the greatest importance in establishing the 

 connection between the uterine epithelium and the syncytium of the villi ; a further 

 action of the syncytium is to convert some of the decidual cells lying between the 

 uterine glands into trophoblastic masses not unlike the invading syncytium itself. 



During earlier stages, stress is also to be laid upon the probability that the 

 secretion of the uterine glands serves as an additional source of nutriment (" embryo- 

 trophe ") to the foetus. 



From the above account it will be seen that there is a considerable histological 

 similarity between the zonary placentae of the cat and Seal ; one notable difference 

 is to be seen in the relatively narrow extent of the gland-layer in the uterus of the 

 Seal, and another in the greater width of the laminae of the placental labyrinth. 



(ix.) The internal ear (PL XXII. fig. 6). — The semicircular canals, utricle, ampullae, 

 and cochlea are well advanced in development, and lie in the cartilaginous rudiment 

 of the osseous labyrinth ; the membranous labyrinth is represented by a somewhat 

 thick connective tissue with a certain amount of elastic tissue entering into its 

 composition. 



A transverse section across one of the semicircular canals in situ shows that the 

 canal is placed very excentrically, lying against one side of the cartilaginous labyrinth, 

 to which the connective tissue fixes it quite firmly. From the projecting part of the 

 canal, strands or bundles of fibres pass to the opposite circumference of the cartila- 

 ginous tube, and, joining here a continuation of the membrane, help to fix the canal, 

 so that practically no contraction of the lumen is possible. The spaces between the 

 fixing strands are filled with perilymph, whilst the canal itself is lined by a somewhat 

 flattened epithelium, which later on secretes endolymph. In the utricle and ampullae 



