On the Nidus and 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, 

 w 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 my researches on 

 that subject, as well in 1844, when I first discovered the 

 Nereis bilineata, as a tenant of the same shell with the her- 

 mit crab, — Pagurus bernhardus, — I saw the eggs of this 

 Nereis extended, and afterwards sheltering under the appen- 



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