145 
generation of the lamprey, the conger eel, &c. 
externally, like so many feet for the progressive motion of the 
worm. The young worm does not remain immured till the 
crysalis covering is expelled, but eats its way out, leaving 
the middle broadest part of this covering sticking in the ex- 
ternal orifice. The total absence of penis and vagina makes 
it difficult to explain what purpose is answered by the copu- 
lation ; from the agitation produced by it through the whole 
of the bodies of the two worms, it seems necessary to dis- 
tribute the ova to the numerous decipimenta in which they 
are met with. 
This is somewhat different from the leech, whose ova are 
deposited in lateral cells, and are squeezed out at lateral 
orifices, covered with a mass of mucus, which at first encloses 
the whole leech. The animal disengages its head by means 
of the teeth, and then, by the wriggling of the body, escapes, 
leaving the mass of eggs and mucus curled up with a hole 
through it in the form of a ball, which the leech deposits upon 
the water, and there the young go through the crysalis state, 
and eat their way out and provide for themselves. 
EXPLANATION OF THE PLATES. 
Plate XV. The Lamprey. 
Fig. 1. Anterior view of a portion of the ovarium and 
testicles of the lamprey, before the breeding season ; mag- 
nified two diameters. 
Fig. 2. A small portion of the same ovarium ; magnified 
five diameters. 
Fig. 3. Posterior view of a portion of the ovarium and 
testicles of the lamprey, in the breeding season ; magnified 
two diameters. 
MDCCCXXIII. 
U 
