MARSUPIAL FISHES. 67 



the mammalia, and in some genera of sharks; an 

 observation which is as old as Aristotle, and which 

 Rondelet represented in one of his plates. Stenonis, 

 in the year 1673, described the embryo of Gahus 

 Icems as connected by means of the placenta ; and 

 Cuvier says briefly, that in the Carcharias the yolk- 

 sac is attached as firmly as a placenta. But on 

 this subject we must not enlarge ; and only repeat, 

 that very ample details on these curious points will 

 be found in the pages already referred to. 



Many of those who read these pages are familiar 

 with the fact, that there is one group of the mam- 

 malia in which the ovo- viviparous mode of deve- 

 lopment, as frequently stated, exists. (Nat. Lib. 

 Mam. xi. 69.) We allude to the Marsupiata, includ- 

 ing the Kangaroos, Opossums, and other families. 

 In connexion with this subject, it is interesting to 

 know that there are true Marsupialia in the class 

 of fishes; that is fish with a marsupium a purse 

 or bag for the safe custody of their young, first in 

 the state of ova, and subsequently in that of fry, 

 which, from their premature extrusion, are altoge- 

 ther unable to take care of themselves. The ana- 

 logy so far is very striking. But a marked differ- 

 ence exists in this respect; that whereas in the 

 mammalia the marsupium is in the female, in the 

 fishes it is found in the males. This provision 

 is met with in various species of the Syngnaihi, 

 or Pipe-fishes, and also in the short round Hip- 

 pocampus, frequently called the Sea-horse. To 



