VIVIPAROUS FISH. 117 



a most complicated and strangely beautiful vas- 

 cular arrangement a network of vessels, the 

 use of which is clearly to convey the lifegiving 

 fluid to the infant fish, and carry it back again, 

 after having served its destined purpose, to be 

 revivified for future use. The way this sac is, 

 as it were, folded, and the different compart- 

 ments made for the accommodation of the embrv- 



/ 



onic fish, is most singular, and very difficult to 

 describe clearly. 



The best illustration I can think of is an 

 orange. You must imagine the orange divided 

 into its regular number of little wedge-shaped 

 pieces, and each piece to represent a fish; that 

 the rind of the orange is a delicate mem- 

 brane, having a globular shape, and easily com- 

 pressed or folded. You now desire to fit the 

 pieces together again in the original orange- 

 shape, but you must begin on the outside of the 

 globular membrane, pressing in with each sec- 

 tion a fold of membrane (remember that each 

 represents a fish) ; when each piece is in its place, 

 you will still have the sac in its rounded form, 

 but the rind or membrane has been folded in 

 with the different pieces. If I have made 

 myself understood, it will be seen that there 

 must be a double fold of membrane between 



