I04 MEDUSA. I. 



therefore, to state their exact number; in well-grown specimens there ma\- be about 200-250 warts. 

 The ectoderm of the warts is somewhat thickened (Plate V, fig. 9). On the abaxial side of some of the 

 warts may be found a small tenon, a rudimentar>' tentacle. 



The marginal vesicles are very numerous, about half as numerous as the warts; they are 

 situated, with a broad base, in the middle of the adaxial side of the warts, close to the velum (Plate V, 

 fig. 9). ■) Marginal vesicles are never found on warts provided with tentacular rudiment. As all of the 

 material at my disposal has been preserved in formalin and left there for several years, the concretions 

 of the marginal vesicles have been dissolved; according to Allman (1871) the number of concretions 

 in each marginal vesicle varies from 4 to 20 in one and the same specimen. 



The velum is well-developed and as broad as the length of the tentacular bulbs. 



In li\ing specimens the tentacles are said to be light pink. 



Though this medusa is ver}- common in the North Sea and adjacent waters, no descrip- 

 tion has been given since 1848 (Forbes). It was first discovered by Ct. Johnston (1833) who made a 

 short description and a somewhat rough figure of the species. A very fine drawing was given by 

 Dal yell (1847 — 4^)- The description delivered by Forbes (1848) was rather incomplete. A few mor- 

 phological remarks are found in the works of Allman (1871) and Bohm (1878). The description in 

 Haeckel's monograph (1879) is based on the descriptions and drawings of Dalyell and F'orbes. -- 

 The records on the occurrence of the species are likewise rather few. It is no wonder, therefore, that 

 Mayer (1910, p. 319) has an entirely incorrect interpretation of the relationship and distribution of the 

 species. Mayer suggests that Tiina bairdii may prove to be the young of Tuna foriiiosa which is 

 found off the Atlantic coasts of New England, and that it is an arctic form occasionall)' appearing at 

 the coasts of Scotland. 



Titiia formosa L. Agassiz reaches twice the size of Ti'iiia bairdii and has about 32 tentacles 

 of three different sizes; according to Bigelow (1913, p- 36) the number of tentacles may amount to 

 39; it has about 100 marginal warts, whereas Tiiiia bairdii, though it is a smaller species, may have 

 more than 200. Mayer (1910, p. 317) and Bigelow (1913, P- 36) confirm the statement of A. Agassiz, 

 that the marginal vesicles in Tiiiia furiiiosa alternate with the warts, being placed in the spaces be- 

 tween the latter; in I'iiiia bairdii they are placed on the warts themselves (see above). The two species 

 may be nearly related to one another, but they are clearly distinct species. 



More peculiar is the suggestion of Mayer (1910, p. 319), that Tiiiia Jiavilabris Eschscholtz 

 might be the young of Tinia foni/osa. It is not very likely that a large species with about 80 short 

 tentacles might be a young stage of a smaller medusa with only 32 tentacles. Tiina flavilabris Esch- 

 scholtz from the Azores is, without au}' doubt, identical with Tiiiia liiciii/aiia Delle Cliiaje from the 

 Mediterranean, Tfflwz/ff/Jr/j being the correct name of the species^. 



Besides the species already mentioned, we know another Atlantic species of Tiiiia, viz. Tiina 

 teiischeri Haeckel from the coast of Brazil, possessing 8 long and 40 short tentacles. 



M A. Agassiz in his description of Tima formom states that the marginal vesicles are situated in the spaces between 

 the warts 



2) The question of the correct name of this species will be discussed in a later work. 



