B VI ] THE HISTORY OF ANIMALS. 140 



near the diaphragm, but in an intermediate position near 

 the spine ; and when they have grown they change their 

 place from this part. The ovum in all fish is not of two, but 

 of one colour ; and it is more white than yellow, both in its 

 early stages, and after the formation of the embryo. 



2. The development of the ovum is different in fish and 

 in birds, in that it has not the umbilical cord which passes 

 to the membrane of the shell ; but only the passage which 

 leads to the yolk in the eggs of birds. The rest of the deve- 

 lopment of the ovum is alike in birds and fish ; for it takes 

 place at the extremity, and the veins have their origin in 

 a similar manner in' the heart ; and the head, and eyes, and 

 upper parts of the body are larger than the rest. As the 

 young fish increases, the ovum continues to diminish, and 

 at last it disappears, and is absorbed, like the yolk in the 

 eggs of birds. The umbilical cord is attached a little below 

 the abdomen. At first the cord is long, but it becomes less 

 as the fish grows, and at last is small, and finally absorbed, 

 like that of birds. 



3. The embryo and the ovum are enclosed in a common 

 membrane, and beneath this there is another membrane, in 

 which the embryo alone is enclosed. Between these mem- 

 branes there is a fluid substance. The nutriment contained 

 in the stomach of the young fish is similar to that in the 

 young birds, partly white, and partly yellow. The form of 

 the uterus must be learned from dissection. This organ is 

 different in different fish, as in the galeode by themselves, and 

 the flat fish by themselves : for in some the ova are attached 

 near the spine to the centre of the uterus, as I observed be- 

 fore, as in scylia. 1 They descend when they begin to increase, 

 when the uterus is double, and are attached to the diaphragm, 

 as in other fish : the ova descend into each division. 



4. The uterus of these fish, and of the other galeode, has a 

 small appendage attached to the diaphragm like a white 

 nipple, which is not present unless they are pregnant. The 

 scylia and the batis have a shell-like substance, which con- 

 tains the fluid of the ovum. In form the shell resembles the 

 tongue of a wind instrument, and hair-like passages are at- 

 tached to the shells. The young of the scylia, which some 

 persons call nebria galei, are born when the shell falls off and 

 bursts. The young of the batis when they are brought forth 



1 Dog fish Squalus stellaris. 



