in certain Aquatic Animals. 337 



simple protuberance on each side of the spine, a little behind the 

 gills. The heart can be distinctly seen pulsating on the under sur- 

 face, and the blood in it is of a red colour. The circulation of the 

 blood can be perceived in the gills, the tail, and on the abdomen, 

 on the under surface of which a large vessel collects many collate- 

 ral streams and returns towards the heart. 



At this period, the surface of the animal produces currents agree- 

 ing in almost every respect with those which take place in the larva 

 of the frog at a corresponding stage of its development. Particles 

 of powder diffused in the water are carried along the surface of 

 the body from its anterior to its posterior extremity ; on the gills 

 they are conveyed along each of the trunks, from the root to the 

 extremity, and apparently with greatest force along the upper and 

 lower surface. The gills also exhibit when cut off the same phe- 

 nomena as in the larva of the frog, advancing through the water 

 with the cut extremity forwards, in a direction contrary to the 

 currents. 



The eggs of the newt being easily procured in every degree of 

 advancement, I next proceeded to inquire at how early a period in 

 the development of the animal the currents are to be perceived. 

 The egg is of an oblong figure, and altogether transparent except 

 the yelk, which is opaque and of a greenish yeUow colour, and is 

 surrounded with a quantity of clear liquid, "the embryo is formed 

 from the yelk, and is at first of the same colour ; it afterwards be- 

 comes elongated, and is covered on the back with dark speckles, 

 uniting at a later period into broad stripes. 



At the period when I was first able satisfactorily to ascertain 

 the existence of a current, the embryo was but little elongated ; 

 the commencement of the gills appeared as a small protuberance on 

 «ach side, elevated but little above the adjacent surface ; the tail 

 did not exist, but its commencement was indicated by the promi- 

 nence of the spine at its posterior extremity. The abdomen was 

 yellow ; the back of a grayish colour, the dark speckles not having 

 yet appeared. When the egg is examined at .this period with a 

 lens of high magnifying power, minute bodies may occasionally be 

 perceived fioating in the liquid with which the embryo is surround- 

 ed. These are drawn towards its imder surface, and immediately 

 hurried onwards a short way in a direction towards the tail. The 

 motion, which exists ^vithin the egg, may be much more distinctly 

 perceived on taking out the embryo, which, however, requires 

 .some nicety, and viewing it in water containing a powdery sub- 

 stance, as in former cases. The current is directed backwards along 

 the under surface of the head and body. It extends only a very 

 short way, and is by no means strong, resembling a good deal what 

 takes place at a more advanced period with parts that have been 

 some time detached from the body of the animal, and, consequent- 

 ly, where the motion has become languid. As the embryo ad- 

 vances in growth, this current gradually becomes stronger, and ex- 



