Parker and Liversidge. — On Mustelus autaix-ticus. 331 



Art. XXXVIII. — Note on the Fatal Memhrancs of Mustelus 



antarcticus. 



By Professor T. J. Parker, F.E.S., University of Otago. 



With an Analysis of tJie Pseitdamniotic Fluid, by Professor 



A. Liversidge, F.R.S., University of Sydney. 



[Bead before the Otago Institute, IWi June, 1889.] 



Plate XIX. 

 Several years ago I connnunicated to the Institute a paper 

 on the gravid uterus of the common dog-fish, or sniooth-houiid 

 (Mustelus antarcticus) /■'■ in which I showed that at the end of 

 pregnancy each foetus is contained in a separate compartment 

 of the uterus, the chambers being separated from one another 

 by complete partitions of mucous membrane, and each being 

 lined by a thin transparent membrane, the jjseudamnion, and 

 tensely filled with a limpid fluid, the ijseudavmiotic fluid, in 

 which the fcetus floats freely. I considered the pseudamuion 

 to be a cuticular secretion of the mucous membrane. 



Although I have dissected a large number of specimens 

 since the time referred to, only one of these has thrown any 

 light on the development of the membranes. It was caught 

 about the middle of December, 1884 : the examples containing 

 ripe foetuses were obtahied in the spring (October). 



When the oviducts were injected with alcohol from th& 

 cloacal end they became filled, showing that the partitions did 

 not exist. On opening, each was found to contain seven eggs 

 of a long-oval form, about 43nim. (Ifin.) in long and 16mm. 

 (fin.) in short diameter. 



Each egg (Plate XIX., fig. 1) was surrounded by a distinct 

 structureless membrane of a light yellow colour, adhering 

 closely to the egg except along one meridian, where it passed 

 oft" at a tangent to the surface, its two closely-applied layers 

 forming a greatly folded sheet fully 30mrn. (12in.) long when 

 stretched out. The membrane is thus a closed sac, the sides- 

 of which are in contact except in the centre, where they are 

 kept apart by the contained egg (tig. 2). 



The membrane was found to adhere so closely to the 

 uterine wall that the eggs retained their position when the 

 uterus was suspended in a jar of spirit, instead of falling to the 

 lower end, as would have been the case if they had been quite 

 free ; indeed, they did not fall out even when the uterus was 

 <)])ened. 



It appears clear that this membrane is the pseudamuion 



" Trans. N.Z. Inst.." vol. xv. (1882), p. 219. 



