1891.] Physiology of Protopterus annectens. 553 



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 ; 

 nephrostomes 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 

 connexion with the testis, quite independently of the excretory ap- 

 paratus. The seminal tubules are directly connected with it, and it 

 opens into the base of the Miillerian duct, the rest of which ap- 

 parently 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 two 

 vibratile flagella attached to the carrot-shaped " head." The genera- 

 tive 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 

 TJrodeles. 



No traces of a sympathetic were found. 



An account of the mode of life of Protopterus during the torpid 

 period is given. The coccoon 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 respiratory current. The 

 source of nutrimeat during the summer sleep lies in the adipose 

 tissue in connexion 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 probability, 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. 



An analysis of^the muscles, by Professor Baumann, shows that 

 they do not retain quantities of the products of nitrogenous waste, 

 as is the case in Elasmobranchs. 



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 to Fishes on the one 

 hand, and to the lower Amphibians on the other, their connexion 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 palaeontological history of the Dipnoi, it is 

 impossible to construct a genealogical tree which will show, with any 

 approach to accuracy, 'the probable connexion between them and other 



