1176 



SCANDINAVIAN FISHES. 



nication with tlie mouth cavity is interrupted, and the 

 hypophysis lies enclosed in the cranial cavity. Sucii is 

 the development in all the higher vertebi'ates. 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 Pehbates fiiscus 

 Goette" has shown that the origin thereof is visible 

 even before the future mouth cavitj' is indicated in any 

 way. There, accordingly, the cerebral hypophysis is at 

 least as primordial an organ as the mouth. In the 

 Lampreys Dohrn" and, after him, Kl'pffer' saw a stage 

 of development (fig. 346, A and B) in which the nasal 

 cavity (N), the hypophysis (Hy), and the mouth cavity 

 (3/) had Ijeguii 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 cpiite different from, a mere 

 apjjendage 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 down^vards 

 over the pharynx. During its growtli and migration as 

 described above the nostril draws -withiii 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 



" Entwickehingsgeschichte der Unk-e, p. 288, tnf. II, tigs. 34- 



' Mittheil. Zool. Stat. Neapel, Bd. IV, p. 172, taf. 18. 



<' Arcli. f. Mikr. Anat., Btl. 35 (1890), p. 537, taf. XXXI, fig. 62. 



'' In the Quart. Jouin. Micr. Sc, N. ser., vol. XXIII (1883), pp. 349, cett., Hubreciit has tried to show that both the liypopliysis 

 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 suffers 

 invagination to receive the former when refracted — 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 epichordal and prechordal part.! 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, offence, 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 vertebrse are developed 

 and their bodies chondrified or ossitied; — and this string, says Hubrecht, was once a sac within which the homologue of the hypophysis 

 might find concealment. 



*■ The Brain and it.^ Functions, Intern. Sclent. Series, vol. XXXVIl, Loud. 1881. 



olfactory apparatus, but only oiw nasal capsule and one 

 nostril. Meckel therefore called theui Mo)iorhhu. 



The hypophysis is accordingly a vei-y primitive or- 

 gan — at least as ancient as the mouth — but in the 

 highest animals has lost its most essential significance/. 

 Similar is the history of the pineal gland. 



In 1881 LuYS published a jjsychology* 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 Eng- 

 land, Fritsch and Hitzig and, after them, Muxk 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 mj's- 

 teries of that life would jiroliably have never been 

 solved by the methods of nattu-al 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 MClleii foreshadowed this, 

 when in his work on the nervous system of the Myxines 

 he chose the cerebral structure of these fishes and of 

 -38. 



