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MESSRS. F. M. BALFOUR AKD W. U. PARKER OK THE 
uncovered by tlie optic lobes, but the major part extends forwards for a considerable 
distance under the optic lobes, as shown in the transverse sections (Plate 24, figs. 46 F 
and G, cb.) ; and its two lobes, each with a prolongation of its cavity, are continued 
forwards beyond the opening of the iter into the fourth ventricle. 
It is probable that the anterior horns of the cerebellum are equivalent to the pro¬ 
longations of the cerebellum into the central cavity of the optic lobes of Teleostei, 
which are continuous with the so-called fornix of Gottsche. 
III. Comparison of the larval and admit brain of Lepidosteus, together with some 
observations on the systematic value of the characters of the Ganoid brain. 
The brain of the older of the two larvae, which we have described, sufficiently 
resembles in most of its features that of the adult to render material assistance in 
the interpretation of certain of the parts of the latter. It will be remembered that 
in the adult brain the parts usually- held to be olfactory lobes were described as the 
anterior cerebral lobes. The grounds for this will be apparent by a comparison of the 
cerebrum of the larva and adult. In the larva the cerebrum is formed of (l) an 
unpaired basal portion with a thin roof, and (2) of a pair of anterior lobes, with small 
olfactory bulbs at their free extremities. 
The basal portion in the larva clearly corresponds in the adult with the basal 
portion, together with the two posterior cerebral lobes, which are merely special 
outgrowths of the dorsal edge of the primitive basal portion. The pair of anterior 
lobes have exactly the same relations in the larva as in the adult, except that in the 
former the ventricles are prolonged for their whole length instead of being confined to 
their proximal portions. If, therefore, our identifications of the larval parts of the 
brain are correct, there can hardly be a question as to our identifications of the parts 
in the adult. As concerns these identifications, the comparison of the brain of our two 
larvae- appears conclusive in favour of regarding the anterior lobes as parts of the 
cerebrum, as distinguished from the olfactory Jobes, in that they are clearly derived 
from the undivided anterior portion of the cerebrum of the younger larva. 
The comparison of the larval brain with that of the adult again appears to us to 
leave no doubt that the vesicle attached to the roof of the thalamencephalon in the 
adult is the same structure as the bilobed outgrowth of this roof in the larva ; and 
since there is in addition a well-developed pineal gland in the larva with the usual 
relations, there can be no ground for identifying the vesicle in the adult with the 
pineal gland. 
Muller, in his often quoted memoir (No. 13), states that the brains of Ganoids are 
peculiar and distinct from those both of Teleostei and Elasmobranchii; but in addition 
to pointing out that the optic nerves form a chiasma he does not particularly mention 
the features, to which he alludes in general terms. More recently Wilder (No. 15) has 
returned to this subject ; and though, as we have already had occasion to point out, 
we cannot accept all his identifications of the parts of the Ganoid brain, yet he 
