On the Nidus mid Young of Pontobdella muricata. 197 
della. Here, then, was a discovery ! The Pontobdella is so 
well known as a parasite on skate and other fishes, that I need 
not describe it. Remembering how little was really known 
about the propagation and early forms of annelides, and of the 
conflicting opinions entertained by various naturalists on the 
subject, I felt quite delighted, — some believing that all pass 
through many changes, from the egg to the adult state ; others 
that there is no change. The tale of the " two travellers" 
came into my mind, " both are right and both are wrong," 
and that at any rate an opportunity was afforded me, if ap- 
pealed to as an umpire, to decide satisfactorily one point in 
the controversy, — namely, that beyond that of growth, the 
Pontobdella passes through no change after leaving the egg. 
The nests are darkish gray, stout and tough, balloon-shaped, 
are deposited in a group, but not in mathematical order. 
Although one showed a worm protruding from the top, this 
was caused by the accidental rupture of the egg ; the natural 
opening for the escape of the young is a circular opening on 
the side. Each nest contains one worm. The shell having 
been long out of the water, all the worms were dead, but in a 
good state of preservation ; they, with many of the nests, are 
in spirits, and only await the time when some one will demand 
them for publication, in the long desiderated history of these 
beautiful, but too long neglected creatures. Having given 
my decision for the no-change man, I must now turn and side 
with those who assert change. From having read many of 
the papers, and seen the figures both of the adult and early 
stages of annelides, by the late Dr George Johnston, and of 
others published in various volumes of the " Magazine of 
Natural History" (unfortunately few of these volumes have 
come in my way), and as well from observations of my own, 
On the luminosity of the sea," published in the " Transac- 
tions of the Eoyal Institution of Cornwall for 1849 and 
1850," where I figured two forms of the young of anne- 
lides which came under my notice during mj researches on 
that subject, as well in 1844, when I first discovered the 
Nereis hilineata, as a tenant of the same shell Avith the her- 
mit crab, — Pagurus hernhardus, — I saw the eggs of this 
Nereis extended, and afterwards sheltering under the appen- 
VOL. II. 2 c 
