412 



PARENTAL CARE AMONG FRESH-WATER FISHES, 



THE DIPNOANS. 



Ill and confined to the Southern Hemisphere are tliree very pecu- 

 liar types of aquatic animal life. One from South America was first 

 described in 183G as a reptile related to the siren of the north and 

 named Lepidosiren; another, from Africa, not long after (1841), was 

 made known as a true fish, and on account of its simple and sup- 

 posedly primitive fashion of limbs styled Protopterns. For a long 

 thne it was a matter of dispute between naturalists whether the two 

 were reptiles or fishes, and no relationship was recognized between 

 them and any other forms, recent or fossil. At last, in Australia, 

 in 1870, was discovered the third tyj^e, and then it became evident 

 that not only had they all relatives in the past, but all their relatives 

 v/ere of the past, and the very distant past. The most recent of 

 those extinct forms, so far as known, lived not only in. old Europe and 

 America, but also in Africa, Asia, and Australia. They enjoyed a 

 world-wide distribution during the Jurassic period and thus early in 

 geological history disappeared from the surface of the earth. Some, 

 of course, must have survived to transmit their blood and likeness to 



Fig. C. — Ncoccratoilus forstcri. After Giinther. 



iheir living relatives, but their fossil remains have not yet been 

 found. There is an extraoi-dinary gaj) between the oldest of the 

 living types (of very late Tertiary age) and the hosts that once 

 I'anged over the globe. The three types are the Lepidosiren of South 

 America, the Profopterus of Africa, and the Neoceratodus of Austra- 

 lia. They and their distant relative, Polypterus^ are immeasurably 

 the nearest of kin to the stock from which alike fishes and reptiles 

 originat(Ml. Two are remarkal)le for the provision which they make 

 for their eggs and young. It is most fitting, therefore, that they 

 should be the first to illustrate j^arental care among fishes. 



The three genera are now segregated into a group named Dipnoi 

 or Dijjneusti, and often called lung fishes, which has been variously 

 estimated to be of subclass, ordinal, or even class value. Here the 

 subclass valuation may be accepted as expressing best the taxonomic 

 importance of the distinctive characters of the group. Among liv- 

 ing fishes the only ones that are at all related to the Dipnoans are the 

 Polypterids or Bicbirs of Africa. These are the representatives of a 



