82 



MEDUS.^. I. 



The investigations, mentioned below, are based on this material and, besides, on material from 

 the Danish waters, vis. from: Nss Sound in the Limfjord; north of the Hirtsholme; Frederikshavn; 

 Lseso Channel; Snoghoj in Lillebelt. 



As will be seen from the list above, I have had at my disposal for investigation abnndance of 

 material from the following regions: New Foundland, West Greenland, Iceland, the Faeroe Islands, 

 Norwav, and Denmark. It was reasonable, therefore, to make use of this material in order to examine, 

 whether the European and the American form are to be regarded as distinct species or merely varie- 

 ties of one and the same species, or whether there might, possibly, prove to be no traceable difference 

 whatever between the two forms. 



With regard to the shape and size of the manubrium, the length and position of the gonads, 

 and the shape of the tentacular bulbs, I have been unable to find any differences. 



According to the literature, the pigmentation of the tentacular bulbs has been estimated as 

 establishing the main difference between Tiaropsis diadeniata and iinilticirrata. Mayer (1910, pp. 258 

 and 259) expresses the difference in the following way: Tiaropsis diadciiiatir. "Entoderm of tentacle- 

 bidbs and of stomach ocher-yellow. Gonads are cream-colored". Tiaropsis iinilticirrata: "... distinguis- 

 hed from the American T. diadiiiiata by the black entodermal pigment of its tentacle-bulbs". "Ento- 

 derm of gonads, stomach, and bell-margin dull-yellow. Ocelli and pigment of tentacle-bulbs black." — 

 Bigelow (1913, p. 32) states as follows with regard to Tiaropsis diadeniata: "The fact that diademata 

 lacks tentacular ocelli has been established on great numbers of specimens, but the tentacular bulbs 

 are not altogether without pigment, for in all the numerous specimens which I have studied they 

 contain a small amount of entodermic pigment of a pale greenish or yellowish-brown color", and with 

 regard to iinilticirrata that, according to the figures at hand, they have "the same entodermic pig- 

 ment, only in much denser masses, and black instead of pale greenish". With regard to the specimens 

 from the northern Pacific, examined by him, Bigelow states as follows (p. 33): "the entoderm of each 

 bulb contains pale greenish, or in some cases greenish-brown, pigment, in a roughly triangular mass"; 

 this pigment is denser tliau that, which the author has observed in Atlantic specimens of diadeniata, 

 but never black as in iinilticirrata. In a footnote (p. 33) he states that in some specimens from Massa- 

 chusetts Bay "the tentacular bulbs were densely pigmented with black granules, thus exactly repro- 

 ducing the European type". These "black granules" probably means the ectodermal pigment granules, 

 which I have likewise found in specimens from both sides of the Atlantic, and which must be well 

 distinguished from the entodermal pigment. 



There can he no d()ul)t, l)ut that the pigment may disappear to a greater or lesser extent 

 owing to the pre.servation. I have .seen specimens from Greenland, Iceland, the F'aeroe Islands, Norway, 

 and Denmark, ])referably when ^jreserved in alcohol, which have retained no other pigment than that 

 of the 8 large ocelli at the marginal vesicles. In better preserved specimens, particularly when pre- 

 served in formalin, from New Foundland, Greenland, Iceland, and Denmark, fine black granules are 

 nearly always found on the surface of the marginal vesicles and the nematocyst-bearing pads of the 

 tentacular bulbs, i. t. on the adaxial and lateral sides of the bulbs. After clearino; in xvlol and under 

 high power this pigment appears to con.sist of accumulations of fine, black granules. Once I conceived 



