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infundibulum, of tori semicirculares in the mid-brain, and of a 
large cerebellum as indications of an affinity between the brain 
of Lepidosteus and that of Teleostei. In the embryological 
section full details are given as to the development of the thala- 
mencephalon, the pineal gland, the cerebrum, and the olfactory 
lobes. 
Organs of Special Sense: Eye.—In the adult eye a vascular 
membrane is described bounding the retinal aspect of the 
vitreous humour. This membrane is supplied by an artery 
piercing the retina close to the optic nerve, and the veins from 
it fall into a circular vessel placed at the insertion of theiris. The 
membrane itself is composed of a hyaline ground substance with 
numerous nuclei. In the developmental section devoted to the 
eye the main subject dealt with is the nature of the mesoblastic 
structures entering the cavity of the optic cup, through the 
choroid slit. It is shown that a large non-vascular mesoblastic 
process first enters the optic cup, and that together with the 
folded edge of the choroid slit it forms a rudimentary and pro- 
visional processus falciformis. At a later period an artery, 
bound up in the same sheath as the optic nerve, enters the optic 
cup, and the vascular membrane found in the adult then becomes 
developed. 
The Suctorial Disk—The structure of a peculiar larval suc- 
torial organ placed at the end of the snout is described, and the 
organ is shown to be formed of papilla constituted by elongated 
-epidermic cells, which are probably glandular (modified mucous 
cells), and pour out a viscid secretion. 
Muscular System.—The lateral muscles of Lepidosteus are 
shown to differ from those of other fishes, except the Cyclosto- 
mata, in not being divided into a dorso-lateral and ventro-lateral 
group on each side of the body. 
Vertebral Column and Ribs.—The early stages in the develop- 
ment of the vertebral column are similar to those in Teleostei ; 
the vertebrze being at first biconcave, and the notochord verte- 
brally constricted. Subsequently an invertebral growth of 
cartilage takes place, derived from the neural and hzemal arches, 
and gives rise to invertebral constrictions of the notochord. 
The embryological part of this section is followed hy a com- 
parative part treated nnder three headings. In the first of 
these the vertebral column of Lepidosteus is compared with that 
of other forms ; and it is pointed out that there are grave diffi- 
culties in the way of comparing the vertebrae of Lepidosteus 
with those of some Urodela in the fact that in Lepidosteus the 
intervertebral cartilages originate from the bases of the arches, 
while in the Urodela they are stated by Gotte to be thickenings 
of a special cartilaginous investment of the notochord, which 
would seem to be homologous with the cartilaginous sheath 
placed in Elasmobranchii and Dipnoi within the membrana 
elastica externa. 
On the other hand, the development of the vertebrae of Lepi- 
dosteus is shown to resemble in most features that of Teleostei, 
from which it mainly differs in the presence of intervertebral 
cartilaginous rings. 
In the second section, devoted to the homologies of the ribs 
of Pisces, the conclusions arrived at are as follows :— 
The Teleostei, Ganoidei, Dipnoi, and Elasmobranchii are 
provided with homologous heemal arches, which are formed by 
the coalescence below the caudal vein of simple prolongations 
of the primitive hemal processes of the embryo. 
In the region of the trunk the hzmal processes and their 
prolongations behaye somewhat differently in the different 
types. In Ganoids and Dipnoi, in which the most primitive 
arrangement is probably retained, the ribs are attached to the 
heemal processes, and are placed immediately without the peri- 
toneal membrane at the insertion of the intermuscular septa. 
These ribs are in many instances (Lepidosteus, Acipenser), and 
yery probably in all, developed continuously with the hemal 
processes, and become snbsequently segmented from them. They 
are serially homologous with the ventral parts of the hzmal 
arches of the tail, which, like them, are in many instances 
(Ceratodus, Lepidosteus, Polypterus, and to some extent in 
Amia) segmented off from the basal parts of the hzemal arches. 
In Teleostei the ribs have the same position and relations as 
thoce in Ganoids and Dipnoi, but their serial homology with the 
ventral parts of the hamal processes of the tail is often (¢.g. the 
Salmon) obscured by some of the anterior hemal arches in the 
posterior part of the trunk being completed, not by the ribs, 
but by independent outgrowths of the basal parts of the beemal 
processes. 
In Elasmobranchii a still further divergence from the primitive 
NATURE 
[ Fan. 26, 1882 : 
arrangement is present. The ribs appear to have passed out- 
wards along the intermuscular septa into the muscles, and are 
placed between the dorso-lateral and ventro-lateral muscles (a 
change of position of the ribs of the same nature is observable 
in Lepidosteus). This change of pos‘tion, combined probably 
with the secondary formation of a certain number of anterior 
heemal arches, similar to that in the Salmon, renders their serial 
homology with the ventral parts of the hamal processes of the 
tail far less clear than in other types, and further proof is re- 
quired before such homology can be considered as definitely 
established. 
Under the third heading the skeletal elements supporting the 
fin-rays of the ventral lobe of the caudal fin of various types of 
fishes are compared and the following conclusions are arrived at. 
1. The ventral lobe of the tail-fin of Pisces differs from the 
other unpaired fins in the fact that its fin-rays are directly sup- 
ported by spinous processes of certain of the hamal arches 
instead ot by independently developed interspinous bones. 
2. The presence or absence of fin-rays in the tail-fin sup- 
ported by hzmal arches may be used in deciding whether 
apparently diphycercal tail-fins are aborted or primitive. 
Urogenital Organs.—With reference to the character of the 
adult urogenital organs, ti.e authors show that for the female the 
descriptions of Miiller and Hyrtl are substantially accurate, but 
that Hyr.l’s description of the generative ducts of the male is 
wholly incorrect. 
They find that in the male the semen is transported from the 
testes by means of a series (40—50) of vasa efferentia, supported 
by the mesorchium. In the neighbourhood of the kidney these 
vasa unite into a longitudinal canal, from which transverse 
trunks are given off, which become continuous with the urini- 
ferous tubuli, The semen is thus transported through the kidney 
into the kidney-duct (segmental duct), and so to the exterior. 
No trace of a duct homologous with the oviduct of the female 
was found in the male, 
With reference to the development of the excretory system, 
the authors have established the following points :— 
1, That the segmental (archinephric) duct is developed as in 
Teleostei. 
2. That a pronephros, resembling in the main that of 
Teleostei, is developed from the anterior end of the segmental 
duct. But they found that the pronephric chambers, each con- 
taining a glomerulus, with which the coiled pronephric tube 
opens, are not, as in Teleostei, completely shut off from the 
body cavity, but remain in communication with it by two richly 
ciliated canals, one on each side of the body. 
3. The pronephros eventually undergoes atrophy. 
4. Some of the mesonephric tubes have peritoneal funnels in 
the larva. 
5. The ovarian sac continuous with the oviduct, is established 
by a fold of the peritoneal membrane, near the attachment of 
the mesovarium uniting with the free edge of the ovarian ridge 
to form a canal, the inner wall of which is constituted by the 
ovarian ridge itself. 
6. The posterior part of the oviduct is not formed until the 
ovarian sac has become developed, and had not been developed 
in the oldest larva (11 centims.) the authors have succeeded in 
obtaining. 
The Alimentary Canal and its Appendages.—In this section 
the authors give a detailed account of the topographical anatomy 
of the alimentary tract in the adult. They have detected a 
small pancreas close to the bile-duct, and call special attention 
to a ventral mesentery passing from the posterior straight section 
of the iritestine to the ventral wall of the body. 
In the embryological part of the section a detailed account is 
given of the development (1) of the pancreas, which is described 
as emerging as a dorsal diverticulum of the duodenum on a level 
with the opening of the bile-duct; (2) of the yolk-sac and 
vitelline duct ; (3) of the spiral valve, which first appears as a 
hollow fold in the wall of the intestine, taking a slightly spiral 
course, and eventually becoming converted into a simple spiral 
ridge. The so-called hyoid gill, which the authors expected to 
find well-developed in the larva, is shown not to be found even 
in the oldest larva examined (26 millims.) 
The last section of the paper is devoted to the consideration of 
the systematic position of Lepidosteus, The Teleostean affinities 
of Lepidosteus are brought into prominence, but it is shown that 
Lepidosteus is nevertheless a true Ganoid. 
The arguments used in this portiou of the paper do not admit 
of being summarised, 
