120 Dr. C. F. Liitken on the Changes of Form in Fishes 



coloration, pattern, squamification, &c. undergo changes so 

 profound and so analogous that we cannot be surprised if 

 ichthyologists on the one hand have created a great number 

 of nominal species, and on the other have not succeeded in 

 separating from each other the very analogous young forms 

 belonging to the two species. The natural consequence of 

 this has been that the connexion between the young and older 

 forms being incajmble of being overlooked by those who had 

 sufficient material at their command, authors have faillen into 

 the extreme opposite mistake, and united the two species, 

 including all the phases of their development, under a single 

 species including a whole series of varieties. The consider- 

 able materials contained in our two zoological museums now 

 combined (the Royal Museum and that of the University) 

 have enabled me to study the distinctive characters of P. paru, 

 BL, and P. aureus, Bl., at all ages, and to confirm, with some 

 modifications, the correctness of the views put forward on this 

 question by MM. Bleeker and Poey. 



Holacanthus ciliaris is subject to analogous changes ; and 

 H. formosus of Castelnau is evidently only a young form of 

 this species. On the contrary, the changes due to age are 

 comparatively insignificant in H. tricolor ; the young indi- 

 vidual represented in pi. v. fig. 6 (of the Danish memoir) has 

 the same large ocellated spot which distinguishes many young 

 Chaitodonts. As to the secondary squamification, Holacanthus 

 ciliaris stands in the same relation to //. tricolor as Pomacan- 

 thus aureus to P. paru. Neither of these genera, so far as we 

 know, passes through the so-called '■'■ Tholichthys'''' phase; and 

 it is hardly probable that this case occurs in them. 



On the other hand, this phase occurs in so great a number 

 of true Chffitodonts, that there can be no doubt it is common 

 to them all. Among the larvae of Cheetodonts or ^'■Tholich- 

 thyes''^ that I have had before me I will mention two. One 

 of them (pi. V. fig. 8 of the Danish memoir) represents, in my 

 opinion, one of the stages of C. sedentarius, Poey [gracilis^ 

 Gth.) , or of some little-known nearly allied species : the other 

 (fig. 10) I have referred to Parachcetodon ocellatus (C. & V.) ; 

 and it would then represent that species in a still younger stage 

 than those at present known, distinguished, among other 

 things, by this peculiarity, that the supraorbital margin termi- 

 nates in a spine directed obliquely sideways and backwards. 

 Like the Chgetodonts, the species of the genera Ephippus 

 {Scato2)hagus) , Hrxrpochirus, and Chelmo, after having com- 

 pletely passed through the '^ ThoUchthys " phase, so far as 

 such a phase exists, undergo modifications, in the form of the 

 body, the coloration, &c., which merit attention, because they 



