1206 
SCANDINAVIAN FISHES. 
mm. These eggs are enveloped in a firm membrane 
and yellowish in colour; the greater part of their con- 
tents consists of yolk. In its hindmost part the said 
ovarian mesentery (mesovarium) presents a totally dif- 
ferent appearance; no eggs are visible here, and the 
mesentery assumes a still more lobate, tuberculate or 
granular form. On microscopical examination no eggs 
are found here, but only vesicles or capsules, contain- 
ing a great number of large cells, many of which are 
in process of division. I. T. Cunningham" was the 
first to express the opinion, based on his investigations, 
that this hindmost part of the mesentery is a mesor- 
chium and contains the male organ. Nay, he even 
considered that he had here found spermatozoa at dif- 
ferent stages of development. Fridtjof Nansen 2, fol- 
lowed up these researches and adopted the theory of 
hermaphroditism, adding that he had observed that, in 
young individuals which had not yet attained a length 
of 320 — 330 mm., the male organ was, as a rule, the 
more developed and contained almost ripe spermatozoa, 
whereas the female organ was more or less undeve- 
loped. Larger (older) individuals he found, on the 
other hand, to contain more developed female organs 
and also large eggs, while the male organ was more 
rudimentary. Hence he concluded that in the younger 
stages of its development Myxine is masculine (prot- 
andric), but afterwards in the older stages feminine. 
But there besides occur, according to Nansen, indivi- 
duals that are males alone. The same investigator also 
gives figures of spermatozoa he had observed in Myxine , 
and asserts that those described by Cunningham are 
not of a true nature. The latter writer has subsequently 
given a new description of the spermatozoa observed 
by him, and insisted upon his priority with respect to 
the theory of hermaphroditism. As I myself too, during 
a series of years (since 1877), have made repeated in- 
vestigations into the structure of Myxine and its mys- 
terious development, I will state that, so far as I can 
find, no distinctly developed male individual thereof 
has hitherto been observed with certainty, and that 
there is much 'to be said for the Cunningham-Nansen 
theory of its hermaphroditism. Considering that I have 
macroscopically examined a great number of Hag-fishes 
and have microscopically prosecuted these investigations 
in many instances that seemed especially remarkable as 
regards the point in question, and this at every season 
of the year, it may appear strange that I have never suc- 
ceeded in finding within the cell-filled vesicles of the so- 
called mesorchium fully developed spermatozoa, but only 
lower and somewhat dubious stages thereof. Yet from 
preparations kindly sent me by Nansen it would seem 
that the structures found by him presented in a high 
degree the appearance of spermatozoa. Phenomena of 
movement, however, have not yet been observed in 
them, and even their development is not fully known®. 
As for the season of impregnation and oviposition, 
these do not appear to be restricted to any fixed time 
of year. All the investigators who have made any 
minute researches into this question are apparently 
agreed that ripening eggs are met with in these crea- 
tures all the year round, but that at the same time in 
other individuals ova may be found at the most different 
stages, from cjuite small, colourless globules, hardly 
distinguishable to the naked eye, to the opaque, yellow- 
ish eggs 10 — 12 mm. long, of an elongated oval form, 
pointed at the ends, enveloped in a horny shell, and 
filled for the greater part by a large yolk. Of such 
ripening, but not yet fully developed eggs a number 
of 10 — 15, up to 26, are as a rule found in the same 
individual, all then exhibiting the same size and ap- 
pearance. These ova, however, as mentioned above, 
are not quite ripe for deposition. There are a few in- 
stances in which specimens have been secured of fully 
developed eggs. In 1859 Allen Thomson figured and 
described in Todd’s Cyclopaedia of Anatomy and Phy- 
siology ova of Myxine that measured about 25 mm. in 
length, had an oval form, and were furnished with a 
firm, horny shell and at each end with a number of 
horny threads, each having hooks (barbs) at the end. 
Some years afterwards J. Steenstrup (Oversigt af d. 
K. Danske Vidensk. Selsk. Forhandl. f. 1863) described 
and figured eggs of similar appearance that had been 
found in a Glutinous Hag. A. W. Malm (Goteb., Bohusl. 
Fauna) also secured ripe eggs 19 mm. long that were 
met with in the stomach of a Cod (thus presumably 
devoured after their deposition); a couple of these were 
described in 1875 by W. Muller in the “Jenaische 
Zeitschrift f. Naturwissenschaft”. Furthermore I. T. 
Cunningham has described in the Quart. Journ. of Micr. 
Sc., N. S., Y. 27, 1887 an egg preserved in the Edin- 
a I. T. Cunningham, Quart. Journal of Microsc. Science, N. S., V. 27, 1887. 
h Fridtjof Nansen, Bergens Museums Aarsberetning f. 1887 (ed. 1888). 
c See further G. Retzius, Biolog. Foreningens Forhandl., Bd 2, No. 8, 1889 — 90. 
