3^2 Dr. Johnson's observations on 
daily notice for a period of at least six months, I may, I pre- 
sume, speak with some decision on this point. It may seem 
perhaps unnecessary to add, that I possess an elegant pre- 
paration, showing this tongue (protruded from the mouth) 
filled with mercury. It is of a cartilaginous structure, and 
admits of great flexibility. It is in length about one-eighth 
of an inch, and is seen, delineated (magnified) in Fig. 5. 
(PI. XVII.) 
The G. tuberculata , is about half a*n inch in length, but when 
fully extended, one inch. It is commonly found in rivulets, 
attached to pieces of wood, stones, &c. A delineation is given 
of its natural size, in a front and back view, in Fig. 1, 2, 3,4. 
It possesses great transparency, and has a fine glossy vitre- 
ous appearance. It is convex above, flattened beneath, and 
somewhat resembles a compressed pear, the tail being very 
broad, and the head tapering towards the extremity, in which 
may be seen six eyes, (Fig. 9. b ,) disposed in two longi- 
tudinal rows. The sides or margin of the body are ser- 
rated. The back is usually of a brown colour, with lighter 
or darker patches, ornamented in the middle with a double 
longitudinal row of white tubercles. (Fig. 9. c .) These 
tubercles are connected together by two black longitudinal 
lines, and are seldom apparent, unless the animal is at rest. 
The belly is generally of one uniform colour, chiefly grey, 
with a slight double black line running longitudinally in the 
centre. 
When this animal is in motion, (to which it is much averse, 
seldom quitting the spot on which it may be affixed,) it is 
observed to throw forward its head to the greatest point of 
extension, and then attach itself by means of the sucker ter- 
