MEDUSAE. I. 



the suspicion that these granules might possibly not be pigment, but foreign matters (dirt, particles 

 of china-ink from the labels). Their mode of distribution, however, contradicts such an apprehension, 

 as they are only found in the said places, vis. on the nematocyst-pads and on the surface of the 

 marginal vesicles; they are wanting on the bulbs of younger tentacles. Similar dark pigment granules 

 may also be found on the surface of the gonads. In the angle between the gonads and the subum- 

 brella unquestionable particles of dirt of quite another appearance are frequently observed. 



It is not always easy to detect the entodermal pigment mass in the tentacular bulbs, and in 

 several cases, when a number of specimens were at hand from one and the same locality, I have been 

 able to find the pigment masses in some specimens but not in others. It is only to be observed when 

 placed above a white support and when lighted from above; it then appears as a triangular mass; as 

 a rule it stands out most distinctly when seen from the adaxial side. Frequently the colour is inde- 

 terminable, but in other cases the colour has been very clear and distinct. As mentioned above Bige- 

 low has found the entodermal pigment in the bulbs of American specimens being pale greenish or 

 yellowish-brown. In the specimens, examined by me, from St. Johns, Newfoundland (Loc. 7) the ento- 

 dermal pigment is yellowish-brown, mostly very clearly visible. In specimens from Greenland, Iceland, 

 and Denmark I have found the same yellowish-brown colour and, frequently, also a distinct green 

 colour in the entoderm of the tentacular bulbs; black entodermal pigment I have never seen. 



It appears, accordingly, that the Tiaropsis from the whole of the North-Atlantic area from the 

 Danish coasts through the waters round Iceland and Greenland to North-America and from the nor- 

 thern Pacific agree completely with regard to the ectodermal as well as the entodermal pigmentation, 

 and thus the character, which has been considered to be the only important feature separating the 

 two "species", does not hold good. 



There can be no doubt, accordingly, but that the European and the American Tiaropsis be- 

 long to the same species. Still the question may arise, whether there might exist a difference between 

 the specimens from the different regions with regard to the size of the bell, the number and arrange- 

 ment of the tentacles, and other measurable characters. Regarding this question I have measured the 

 diameter and counted the tentacles in a large number of specimens, in so far as they are sufficiently 

 well-preserved for such purpose. I have found that within each of the areas in question there appears 

 a considerable variation concerning these characters, but that the average figures for the various areas 

 are so near each other, that we can hardly speak about local varieties. As the investigation may pos- 

 sibly have some importance from a variation-statistical point of view, I am going to give a short 

 account of the results. 



One of the characters I wanted to examine, was the relation between the number of tentacles 

 and the diameter of the bell. It is evident that measurements of preserved medusae have to be used 

 with caution, because the individuals always contract at the preservation and not always to the same 

 degree. The figures in the tables (IX and X), representing the diameter, must therefore be used with 

 reservation, but they seem to indicate that the specimens from the different areas agree in the main 

 with regard to the said feature. 



In table IX is represented the correlation between the number of tentacles and the diameter 

 of the bell of specimens from the different regions; the general results of the table have been gathered 



