20 



NATURE 



{Nov. I, 1888 



the energy of Dr. J. Beard, who, assisted by a grant from the 

 Royal Society, hoped by procuring Protopterus in sufficient num- 

 bers, and keeping them alive under suitable conditions, to be able 

 to study their development. My thanks are therefore due to 

 Dr. Beard, as well as to Prof. Wiedersheim, for the specimens I 

 have made use of. 



The clods of earth in which the animals were inclosed in their 

 torpid state having been opened up, they were found to contain 

 about one hundred living specimens, varying in length from about 

 8 to 80 cm. These were kept in a tank in the Botanical Garden, in 

 water which stood at a temperature of 18° Reaumur. They were 

 fed with water-snails, earth-worms, Entomostraca, and small fishes, 

 the last of which they seemed to prefer. But the abundant 

 nourishment with which they were supplied did not prevent 

 them from killing one another, so that at the date of writing only 

 a small proportion still remain alive. In order to prevent this 

 cannibalism, we should have isolated them by means of wire- 

 netting, had it not been thought that this would greatly lessen 

 any chance of obtaining embryos. Their vitality is very remark- 

 able : after having been bitten severely, and having consequently 

 lost much blood, they will usually live for some days. 



The structure of the "cocoon," and the position of the animal 

 within it, have already been described by Wiedersheim, ^ and in 

 this connection I have only one point to add with regard to the 

 respiration of Protopterus during its torpid state. Although in 

 one or two of the specimens we noticed a slight redness of 

 the tail, I doubt very much whether, as Wiedersheim supposed, 

 the tail serves as a respiratory organ during this period. A close 

 examination of that part of the cocoon-membrane which closes 

 the bottom of the earth-tube, and which overlies the animal's 

 nose, showed that no additional respiratory apparatus was 

 necessary. Looking at this membrane from the outer side, the 

 small aperture described by Bartlett and Krauss can be plainly 

 seen. On the inner side, the rim of this aperture is produced 

 into a funnel-shaped tube, the free end of which lies between 

 the lips of the animal. Consequently, by means of this pipe, the 

 Protopterus can inhale and exhale air during its long sleep. On 

 being removed from the cocoon, moreover, the lungs were 

 always found to be greatly distended and full of air, bubbles of 

 which were immediately given off into the tank in which the 

 specimens were placed. In all probability the above-mentioned 

 tube is produced by suction, when the secretion which gives rise 

 to the cocoon is still soft. The curious squeak which Protopterus 

 makes when set free from the cocoon has been noticed by other 

 observers. 



In addition to dissections, and sections of various individual 

 parts, I have made a complete series of transverse sections — in 

 all about 2100 — of a small female specimen : these are extremely 

 instructive. 



Integuvietit. — Each outer cell of the epidermis is provided 

 with a cuticular cap, and the whole of the epidermis is closely 

 packed with goblet cells, which are less numerous on the paired 

 fins than on the body, where they are less than the diameter of a 

 single one apart. Multicellular glands, very simular to those of 

 Amphibia, are also present here and there throughout the body, 

 and are particularly numerous on the snout. Nests of lymphatic 

 tissue are present beneath the epidermis in some regions. 



Aluscles. — The chief point of interest I wish to mention con- 

 cerning the muscles is that they, more particularly the great 

 lateral muscles of the tail, serve as stores of nutriment for the 

 animal during its torpid state. A similar phenomenon has been 

 described by Miescher-Riisch in the salmon during the spawn- 

 ing season."'' 



The muscular tissue in places shows histologically all stages of 

 retrogressive metamorphosis, and owing to this process, the 

 leucocytes are able to absorb its broken-down remnants, which 

 can be plainly recognized within many of the leucocytes which 

 simply swarm into the muscles in these regions. In some parts 

 the muscle is completely eaten away, so that nothing but the 

 perimysium is left. 



Nervous System. — An account of the structure of the nerves, 

 with their numerous spindle-shaped nuclei, and of the remarkable 

 nerve- cells, I cannot give here, and I also reserve at present a 

 description of certain of the cranial and spinal nerves, and of the 

 nerve-supply of the fins. I must, however, mention that the 

 pulmonary nerve crosses its fellow at the base of the lungs, and 

 then runs along the dorsal surface of the lung of the other side. 



' Anat. Anzciger, II. Jahrgang, 1887 ; and Proc. Brit. Assoc, 1887. 

 2 "Ueber das Leben des Rheinlachses im Siisswasser," Archiv.f. Anat. 

 u. Physiol., 1881. 



A lateral nerve is situated on either side of the notochord, beneath 

 the muscles, at the point where the dorso-lateral and ventro- 

 lateral muscles meet. The spinal ganglia lie outside the canal. 

 No trace of a sympathetic could be detected. 



Sensory Organs. — Tntcgumetitary Sense-organs. — These are 

 very numerous in the head, and in the body they are not 

 restricted to the main Literal line, but are present in regions 

 above and below it also. They are situated within the epi- 

 dermis, external to the scales. The moisture necessary for their 

 persistence during the torpid period is produced by the gland- 

 cells of the integument. A mass of lymphatic tissue is 

 usually present directly beneath each : this may be concerned 

 with its nutriment, for it is known that in Amphibians these 

 organs are continually undergoing regeneration. I have been 

 unable to discover any sensory organs in the integument of the 

 paired fins, and the function of these curious filamentous 

 appendages, with their large nerve-supply, is still problematical. 



The pharynx is provided with sensory organs similar in 

 structure to those of the integument. 



Olfactory Organ. — The structure of the nose is very compli- 

 cated. In the presence of accessory cavities, it resembles that of 

 Amphibia, but in the folding of the epithelium it is more similar 

 to that of fishes. The main cavity gives rise to dorsal and 

 lateral extensions, the latter corresponding closely with the 

 "pars maxillaris " of Amphibia. Posteriorly, the main cavity 

 branches into a number of tubes, each with a small lumen ; these 

 in transverse section resemble gland-tubes cut across. The 

 olfactory cells are in some parts diffuse, in others arranged in 

 groups, as in many fishes and Amphibians. 



No special glands are present in connection with the nose, as 

 one would naturally expect. But the moisture necessary for the 

 olfactory cells is probably produced by the numerous goblet 

 cells which are present in the epithelium of the mouth and that 

 lining the anterior and posterior narial passages. This may ex- 

 plain the peculiar position of the anterior nostrils, which open 

 beneath the upper lip. 



Eye. — No gland is present within the orbit. The lens is 

 globular and relatively large, filling up the greater part of the 

 posterior chamber, so that there is little space left for the 

 vitreous body. The sclerotic is fibrous, but a few cartilage cells 

 can be recognized in those regions in which the eye-muscles are 

 inserted. The choroid is rudimentary, and contains no pigment, 

 and there is no iris or pupil, the pupillary membrane being con- 

 tinuous over the front of the lens. The epidermis thins out 

 slightly over the eye, and in this region the goblet cells are 

 smaller and less numerous. The dermal fibres are directly con- 

 tinued on the one hand into the representative of the cornea, and 

 on the other into the sclerotic. Processes of the pigment cells 

 of the retina can be seen passing between the rods and cones. 

 No trace of a processus falciformis could be seen. 



Alimentary Canal.— Zi>5. — No muscles are present in 

 connection with the lips, as is stated to be the case by Ayers. ^ 

 Beneath the epidermis they consist of a curious embryonic con- 

 nective tissue very rich in nuclei, similar to that found in the 

 snout and tongue. 



Tongue. — -The tongue- is covered with numerous filiform 

 papilljE in older specimens, the histological structure of which I 

 have not yet examined. None are present, however, in the 

 sections of a younger specimen. Goblet cells are very numerous 

 in the epithelium, which is folded so as to give rise to a number 

 of simple gland-like sacs. No sense-organs can be seen in my 

 sections. The extrinsic muscles are, on either side, (i) a large 

 hyoglossus, and (2) a small band-like branchioglossus. There 

 are no intrinsic muscles, the whole of the substance of the 

 anterior part of the tongue beneath the epithelium consisting of 

 the connective-tissue referred to above. 



On the floor of the mouth, in front of the tongue, and between 

 the two cusps of the mandibular teeth, is a curious tube-like 

 epithelial organ which apparently opens by a small aperture 

 near its posterior end into a median groove of the oral epi- 

 thelium. This tube is lined by columnar epithelium with 

 goblet cells. 



Thyroid. — The thyroid is a small bilobed organ, situated 

 between the connective-tissue and muscular portions of the 

 tongue. Its epithelium is flat, and the tubules contain a colloid 

 mass which stains deeply. 



Thymus. — The well-developed thymus consists of adenoid 

 connective-tissue with leucocytes, and lies on the dorsal side of 



' "Beitragez. Anat. ii. Physiol, der Dipnoer,"/<'«- Zeitschr.f. Natu>~w!ss., 

 Bd. 18, 1885. 



