218 Mr. J. T. Cunningham on some 



S" 



the body-cavity is formed as a " schizocoel," and never has 

 any connexion with either the lumen of the intestine or the 

 gastrula-cavity or the segmentation-cavity. In fact I can 

 state, from my own observations, that the pericardial cavity 

 has no communication with the perivitelline cavity ; and the 

 same conclusion is confirmed by Shipley's observations on 

 Petromyzon. In the nine quarto pages which M'Intosh and 

 Prince devote to the development of the heart and blood- 

 vessels I can find nowhere any mention of the fact that the 

 auricle is open posteriorly to the perivitelline blood-sinus, which 

 has the same position as the segmentation-cavity of an earlier 

 stage. It seems as though these observers had either over- 

 looked the posterior opening of the heart or had mistaken it 

 for an opening into the pericardium *. 



Chromatophores. 



Chromatophores may be developed both in larval and adult 

 Teleosteans in other parts of the mesoblastic tissues besides 

 the derma ; but as a rule the coloration of the fish depends 

 chiefly on the chromatophores present in the skin. In all the 

 species which have come under my own observation the 

 chromatophores in the skin of the larva or embryo at their 

 earliest appearance are in all respects similar to those of the 

 adult both in colour and in structure. For instance, in the 

 adult mackerel there are black chromatophores and green 

 chromatophores, and in the larva also black and green chro- 

 matophores appear. Similarly in the Pleuronectidee the colour 

 of the adult depends on the distribution of the black and 

 yellow or orange chromatophores. I am leaving the irido- 

 cytes, whose colour-effect does not depend on pigment, out of 

 consideration. In larval flat-fishes the only chromatophores 

 developed are the black and the yellow or orange. Professor 

 M'Intosh, in his review of my book on the sole, says, " The 

 pigment of the larval sole in Scotland appears to differ mate- 

 rially from that of the larval sole at Plymouth, since it is 

 not truly yellow, but dull stone-grey or dull yellowish white, 

 and this afterwards changes into the ochreous hue so charac- 



* It must be added here that what I and most other writers on this 

 subject have called the " pericardium " in the Teleostean embryo or larva 

 is not exactly the same thing as the pericardium of the adult. I believe 

 that the embryonic pericardium is merely a portion of the general coelom 

 or body-cavity, the first part of that cavity to be developed ventrally. I 

 believe that as the yolk disappears this embryonic pericardium extends 

 backwards and becomes continuous with the lateral body-cavities, the 

 adult pericardium being afterwards separated from the general body- 

 cavity. 



