Parkek. — On the Gravid Uterus of Mustelus antarcticus. 219 



Art. XXVIII. — On the Gravid Uterus of Mustelus antarcticus. 

 By T. Jeffery Parker, B.Sc. 

 [Read before the Otago Institute, 31st October, 1882.] 

 Plate XXX. 

 The viviparous dog-fish Mustelus is remarkable for the fact that in one of its 

 species, M. levis of the northern seas, a vascular connection is established 

 between the foetus and the mother by the yolk-sac of the former entering 

 into close contact with the wall of the uterus, and thus forming an " um- 

 bilical placenta." This arrangement becomes all the more remarkable from 

 the circumstance that in the other species of the genus no such connection 

 obtains. 



In Gunther's " Catalogue of Fishes," as well as in his more recent 

 work, " The Study of Fishes," the common southern Mustelus, M. ant- 

 arcticus, is merely said to be, like M. vulgaris and other northern forms, 

 devoid of an umbilical placenta, from which one would naturally expect to 

 find the foetuses lying freely in the uterine cavity, as in other viviparous 

 sharks — e.g., Scymnus or Acanthias. I was therefore considerably surprised 

 to find, on dissecting a gravid female of M. antarcticus a week or two since, 

 that the relations between the mother and the foetus were nothing like so 

 simple as I had expected, but that, just as the Mustelus levis furnishes a 

 sort of foreshadowing of tbe true placenta of mammals, so M. antarcticus is 

 provided with membranes which, although formed from the maternal and 

 not from the foetal tissues, foreshadow in a remarkable manner the chorion 

 and the amnion. 



The specimen referred to, and others dissected subsequently, were evi- 

 dently near delivery, since the foetuses (see fig. 1) were large and perfectly 

 formed, and their yolk-sacs (yk. s) were reduced to the size of a small pea. 

 On opening the abdomen the uteri were at once noticeable from their great 

 transparency and extreme tenseness : the foetuses could be plainly seen 

 through their walls, and the uteri themselves had the appearance of being 

 distended with fluid. By squeezing the uterus from the outside each foetus 

 could be only very slightly displaced ; it was evident that they were con- 

 fined in some way, but not by actual attachment to the uterus. 



The explanation of these appearances was at once evident on opening the 

 uterus. Each foetus was then seen to be enclosed in a separate compart- 

 ment, filled with a colourless fluid, in which it floated freely. The partition 

 walls between adjacent compartments are evidently quite impervious, so 

 that there was no communication between them, nor between the anterior 

 compartment and the cavity of the Fallopian tube (fig. l,fl.t.) or the posterior 

 compartment and the cloaca. 



