I40 



NA TURE 



[June ii, 1891 



in the research, a short preliminary notice, without illustrations, 

 was published in the following autumn {Berichte d. Naturforsch. 

 Gesellschaft zu Freiburg i. Br., vol. iv. 1888 ; see also Nature, 

 vol. xxxix. p. 19) This notice merely forms the basis of the 

 present paper, in which the whole subject has been worked out 

 in greater detail. A number of new facts are recorded, some of 

 the author's earlier conclusions modified, and the paper illus- 

 trated with u plates containing 71 figures. 



With the exception of certain special details, the structure of 

 the skeleton and of the nervous and muscular systems are not 

 described, the paper consisting mainly of an account of other 

 organs which have not received so much attention from previous 

 observers, and of a comparison of Protopteriis with the other 

 genera of Dipnoi, so far as their structure is known, as well as 

 with other Ichthyopsida. 



A number of details with regard to the habits of Protopterus 

 in captivity are given. 



The paired extremities show no connection with the cheiro- 

 pterygium, and, in spite of their considerable nerve-supply, are 

 evidently greatly degenerated structures as regards their free 

 portions. Sensory organs are not present on them, and they 

 therefore cannot have a tactile function. Their distal ends, like 

 the apex of the tail, are very variable, and can undoubtedly be 

 reproduced when lost by accident. The tail is almost certainly 

 not primarily diphycercal, and shows signs of a possible origin 

 from a heterocercal form. 



The epidermis on the whole most nearly resembles that of 

 Perennibranchiate Amphibians, and gives rise to simple multi- 

 cellular glands, as well as to very numerous closely-packed 

 goblet-cells, which produce the gluey secretion as well as the 

 main substance of the capsule which surrounds the animal during 

 the torpid state. 



The integumentary sense-organs are similar to those of fishes 

 and larval Amphibians. The relations of the sensory organs of 

 the trunk are similar to those seen in young stages of Fishes and 

 in Amphibian larvae, while in the case of the head they resemble 

 those which are typical for adult Fishes. End-buds, similar in 

 structure to the taste- buds of Fishes and Amphibians, are present 

 on the tongue and oral epithelium. 



As regards its general structure, the olfactory organ most 

 nearly resembles that of Elasmobranchs, but the presence of 

 posterior nostrils raises it to a higher level. The position of the 

 anterior nostrils beneath the upper lip is probably to be accounted 

 for as an adaptation in connection with the torpid state. Four 

 straight and two oblique muscles are present. The sclerotic is 

 fibrous in young animals, and islands of cartilage first appear at 

 the points of insertion of eye-muscles, and then gradually extend 

 so as to chondrify the whole. The eye resembles that of Am- 

 phibians ; a processus falciformis and campanula Halleri are 

 absent, and no ciliary muscles were observed, though possibly 

 present ; almost all the pigment of the eye is ectodermic. 



No specialized glands are present in connection with the 

 greatly folded epithelium of the oral cavity. The lips contain 

 no muscles. The tongue, as well as the palate, is covered with 

 blunt conical papillae, on which the taste-buds are situated. A 

 horny cap is developed over each tooth from the overlying epi- 

 thelium, which apparently becomes cut through by the sharp 

 edges and points of the teeth, and which probably corresponds 

 to the cuticida dentis. The thyroid and thymus are described. 



A ventral, as well as a fenestrated dorsal, mesentery is present 

 supporting the intestine. The author compares the so-called 

 urinary bladder (" cloacal csecum") with the "processus digiti- 

 formis " of Elasmobranchs. A spleen and pancreas are present, 

 embedded in the thin walls of the stomach, and extending on to 

 the proximal part of the intestine ; they are covered externally by 

 sparse muscular fibres as well as by the peritoneum. The rela- 

 tions of the pancreas therefore most nearly resemble those met 

 with in Ganoids and certain Teleosteans. The pancreas is 

 deeply pigmented, and its ducts open into the bile-duct. The 

 pigmented walls of the intestine and the spiral valve are very 

 thick, owing to the abundance of lymphoid tissue contained 

 within them. With the exception of the bursa entiana, the in- 

 ternal walls of which are raised up into a number of deeply 

 pigmented oblique folds, the whole of the mucous membrane of 

 the stomach and intestine is perfectly smooth, and there is no 

 indication of any differentiated gastric or intestinal glands. 



Cilia are present on the epithelium throughout the stomach 

 and intestine. A layer of small-celled lymphoid tissue directly 

 underlies the epithelium. In the spleen and lymphoid organs of 

 the intestine two kinds of tissue are present. Large migratory 



NO. I 128, VOL. 44] 



cells are present in both kinds of tissue, many of which inclose 

 yellowish granules. Gradations between these and rounded 

 cells of a deeper yellow or brown colour can apparently be made 

 out, and cells appearing to be intermediate forms between these 

 and the ordinary black, branched pigment cells can also be seen. 

 It seems probable that the yellow granules mentioned above are 

 due to the disintegration of red corpuscles, which are ingested by 

 leucocytes, and then undergo some change, whereby the latter 

 gradually pass into the condition of black pigment cells, which 

 migrate through the epithelium, and are so got rid of. The 

 muscular layers are very thin. 



The question as to the mode of digestion and absorption of the 

 food in Protopterus is discussed. 



The branchial apparatus shows signs of considerable reduc- 

 tion. The pulmonary apparatus, on the whole, more nearly 

 resembles the air-bladder and its duct of certain Ganoids than 

 the lungs and laryngo-tracheal chamber of Amphibians. The 

 pulmonary branches of the vague cross one another at the base 

 of the lungs. 



The blood is remarkable for the large size of its elements, 

 which is only exceeded in the case oi Proteus and iii7-en, as well 

 as for the large proportion of white corpuscles in comparison 

 with the red ones. Two forms of the former are described. 

 The chief points of interest with regard to the blood-vessels 

 are : (i) the paired pulmonary artery, the left supplying the 

 ventral, and the right the dorsal, aspect of the lungs ; (2) the 

 single post-caval and persistent left posterior cardinal vein ; and 

 (3) the single caudal vein, giving rise to a right and a left renal 

 portal. 



No external sexual differences could be observed, and amongst 

 the specimens examined, females were the more abundant. 

 The urino- genital organs are surrounded by masses of tissue 

 resembling the large- celled lymphoid tissue of the gut, but 

 differing from the latter in becoming largely converted into 

 adipose tissue. The kidneys probably represent the mesonephros,. 

 and their duct the Wolffian duct ; nephroslomes are absent. 



In unripe males, delicate Miillerian ducts are present. The 

 sperm is conducted to the exterior by a duct, which is probably 

 formed in connection with the testis, quite independently of the 

 excretory apparatus. The seminal tubules are directly connected 

 with it, and it opens into the base of the Miillerian duct, the 

 rest of which apparently aborts completely. Unlike most of 

 the tissue elements, which are very large, and closely resemble 

 those of the Amphibia, the spermatozoa are very minute, and 

 are remarkable in possessing tzvo vibratile flagella attached to 

 the carrot-shaped " head." The generative organs of the female 

 bear a striking resemblance to those of Amphibians. The 

 oviduct corresponds to the Miillerian duct ; the epithelium 

 covering its internal folds shows signs of degeneration similar 

 to those which have recently been described amongst Urodeles. 



An account of the mode of life of Protopterus during the 

 torpid period is given. The cocoon is provided with a "lid," 

 perforated by a hollow funnel-shaped tube, which passes between 

 the lips of the animal, and thus forms a passage for the respira- 

 tory current. The source of nutriment during the summer 

 sleep lies in the adipose tissue in connection with the gonads- 

 and kidneys and alongside the notochord in the tail, as well as 

 in the lateral muscles, some of which, especially in the caudal 

 region, undergo a granular degeneration. Very probably the 

 latter is the precursor of the fatty degeneration, and, in all prob- 

 ability, leucocytes are the active transporting agents of the 

 degenerated material. This assumption would help to explain 

 the large development of lymphoid tissue in the body of the 

 animal. 



The systematic position of the Dipnoi is briefly discussed in 

 the light of the new facts brought forward in the present paper. 

 Although the Dipnoi present many points of resemblance ta 

 Fishes on the one hand, and to the lower Amphibians on the 

 other, their connection with any living forms of either class is 

 probably a very distant one, and it is inadvisable to classify 

 them amongst the Fishes. Owing to the absence of ontological 

 evidence, and to the incompleteness of our knowledge of the 

 palseontological history of the Dipnoi, it is impossible to con- 

 struct a genealogical tree which will show, with any approach to 

 accuracy, the probable connection between them and other 

 Ichthyopsidan types. The most that can be said at present, with 

 anything like certainty, is that the Dipnoi are the isolated sur- 

 vivors of an exceedingly ancient group, which was probably 

 related to the ancestors of existing Fishes and Amphibians. 

 Amongst the former, the connection seems to be closest to the 



