1176 
SCANDINAVIAN FISHES. 
nication with the mouth cavity is interrupted, and the 
hypophysis lies enclosed in the cranial cavity. Such is 
the development in all the higher vertebrates. In the 
lower, on the other hand, as for instance in the frogs, 
the cerebral hypophysis appears still earlier, before the 
mouth cavity is developed enough to contain the origin 
of this appendage within its region. In Pelobates fttscus 
Goette" has shown that the origin thereof is visible 
even before the future mouth cavity is indicated in any 
way. There, accordingly, the cerebral hypophysis is at 
least as primordial an organ as the mouth. In the 
Lampreys Dohrn 0 and, after him, KupffeiT saw a stage 
of development (tig. 346, A and B) in which the nasal 
cavity (N), the hypophysis (////), and the mouth cavity 
(M) had begun to appear on the under surface of the 
rudimentary head in the form of three uniserially (in a 
sagittal row) arranged impressions of the ectoderm. But 
here the homologue of the hypophysis becomes much 
more than, and something quite different from, a mere 
appendage of the brain. Such an appendage is indeed pre- 
sent in the Lampreys; the said rudiment here too grows 
in a tubular form upwards and backwards towards the 
tip of the notochord, but it also moves upwards round 
the snout, continually growing, and becomes the so- 
called nostril of the Lampreys, which throughout their 
life opens on the dorsal side of the head and thence 
extends in a tubular form backwards and downwards 
over the pharynx. During its growth and migration as 
described above the nostril draws within its limits the 
true olfactory apparatus (fig. 343, n), a capsule imper- 
fectly divided internally into two chambers, and deve- 
loped from the nasal cavity (fig. 346, B ; N) that once 
lay before the rudiment of the hypophysis. In this 
manner the Cyclostomes attain a unique position among 
the vertebrates. They possess, it is true, a well-developed 
olfactory apparatus, but only one nasal capsule and one 
nostril. Heckel therefore called them Monorhini. 
The hypophysis is accordingly a very primitive or- 
gan — at least as ancient as the mouth — but in the 
highest animals has lost its most essential significance L 
Similar is the history of the pineal gland. 
In 1881 Luys published a psychology * 6 as the result 
of his works on the brain and its functions, giving us 
in a very popular way means to understand the relation 
between the different parts of the brain. By numerous 
and successful sections he traced the course of the nerve 
fibrils to the brain and within this to the connexion 
between its countless ganglion cells. Contemporaneously 
with these and other anatomical works Ferrier in Ene- 
land, Fritsch and Hitzig and, after them, Munk in Ger- 
many, had published their famous attempts to discover 
in the superficial layers of the brain the so-called psy- 
chomotor centres and to define their limits. These and 
other later researches in many points have modified the 
views advanced by Luys, especially as to the arrange- 
ment of the sensorial tracts, but for our present purpose 
we may leave those discrepancies out of sight. The 
brain of the higher vertebrates, with its rich psychical 
life, is, however, of so complex a nature that the mys- 
teries of that life would probably have never been 
solved by the methods of natural history, had not more 
simple material been placed at the investigator’s disposal. 
The study of the lowest fishes in particular has led to 
the one comprehensive conclusion after the other. Thus 
we shall, no doubt, be able at length to trace the ori- 
gin of different psychical faculties in connexion with the 
different development of some part or other of the brain. 
Already in 1840 Johannes Muller foreshadowed this, 
when in his work on the nervous system of the Myxines 
he chose the cerebral structure of these fishes and of 
a Entwickelungsgeschichte der Unke , p. 288, taf. II, figs. 34 — 38. 
6 Mittheil. Zool. Stat. Neapel, Bd. IV, p. 172, taf. 18. 
c Arch. f. Mikr. Anat., Bd. 35 (1890), p. 537, taf. XXXI, fig. 62. 
d In the Quart. Journ. Micr. Sc., N. ser., vol. XXIII (1883), pp. 349, cett., Hubrecht has tried to show that both the hypophysis 
and the notochord are inheritances from the worm-like predecessors of the vertebrates. The hypophysis, he contends, represents the proboscis 
of the flat- worms and the notochord their proboscidian sheath. At the limit between the proboscis and the sheath- — where the latter sutlers 
invagination to receive the former when retracted — lies. the principal mass of the Platyelminth nervous system; and at the corresponding 
point in the skull of the lower vertebrates, at the limit between the epicliordal and prechordal parts of the brain, there too do the notochord 
and hypophysis meet each other. 
Neither the hypophysis nor the notochord would thus be peculiar to the vertebrates; they would have their prototypes in the lowest 
worms. The hypophysis lies under our brain in the most protected spot throughout our body, as even Galen remarked, as if it were a most 
important and delicate organ; but it lies there, according to Hubrecht, merely as a relic, a vestige of an organ which serves the lowest 
worms for purposes of touch, otfence, and defence. In us adults the notochord has entirely disappeared; but during our foetal life and that 
of the other higher animals, as well as in the adult state of lower vertebrates, this string is the axis round which the vertebrae are developed 
and their bodies chondrified or ossified; — and this string, says Hubrecht, was once a sac within which the homologue of the hypophysis 
might find concealment. 
e The Brain and its Functions , Intern. Scient. Series, vol. XXXVII, Bond. 1881. 
