70 



NATURE 



{Nov. 17, 1887 



ON SOME OF THE AFFINITIES BETWEEN 

 THE GANOIDEICHONDROSTEI AND OTHER 

 FISHES. 



T'^HE group of Ganoiclei Chondrostei has hitherto been regarded 

 •^ as one developed during the latest period of the history of 

 the earth. Its structure is so different from that of other classes 

 offish that its relationship with them cannot be easily detected. 

 The zootomic and embryological works of the last ten years, 

 and especially the works of Zalensky in Odessa, Parker in 

 London, Davidoff in Munich, and van der Wighe in Holland, 

 have brought together many important facts as to the organiza- 

 tion and development of these interesting animals, but the in- 

 formation provided by these writers is either fragmentary or not 

 full enough, and long study and labour will be required before 

 it can be satisfactorily summed up and completed. 



During the last two years I have studied the anatomy of 

 Acipenser ruthenus, the commonest representative of the Aci- 

 penseridse to be found here ; and although my work is far from 

 being completed I may beg the reader's attention to some 

 interesting facts, which must, I think, be taken into considera- 

 tion by those who try to settle the question as to the relationship 

 of the Ganoidei Chondrostei to this or to that group of fishes. 



We may begin with the teeth of these fishes, as an indication 

 of great value, which served to distinguish this group from other 

 Ganoidei. Teeth have been found in Polyodon folium, a 

 member of the Ganoidei Chondrostei, inhabiting the rivers of 

 North America ; it has been thought that they might also be 

 found in Psephtmis gladius of the River Yang-tse-kiang, in 

 China ; and Prof Zalensky has found them in Acipenser ruthenus, 

 at the age of from three weeks to three months. I have had 

 the good fortune to find teeth in a'most all the Ganoidei Chon- 

 drostei of the different ages that I have examined, but they were 

 palatine teeth, not mandibular or maxillary teeth. I have 

 discovered and studied the palatine teeth in a two-months- 

 old sterlet ; in an Acipenser stellatus of from seven to eight 

 months old ; in a Scaphirhynchus kaufmannii from Amu- 

 Daria of a year old ; in a grown Scaphirhynchus fedschenkoi 

 from Sir-Daria ; and in full-grown Polyodon folium. 



The relationship of the dimensions of the snout offish to the age 

 at which teeth can be found is very interesting. The long and 

 flat snouted Acipenser slellahts has teeth to a more advanced age 

 than the short and narrow snouted sterlet ; the teeth of a wide- 

 snouted Scaphirhynchus not attaining a good development but are 

 preserved until maturity ; the spade-snouted Polyodon preserves 

 its teeth during the whole of its life. In all the other repre- 

 sentatives of Acipenser and Scaphirhynchus can be found at 

 any stage traces of palatine teeth in the shape of two similar 

 ■prominences, which, by their structure, can be distinguished from 

 the surrounding parts of the mouth. 



This dependence of a long preservation of teeth on the de- 

 velopment of the snout of Ganoidei Chondrostei, together with 

 the geographical distribution of these fish, shows the greater 

 antiquity of the tooth-preserving kinds of Scaphirhynchus and 

 Polyodon, than of the Acipenser. Species of one kind, in- 

 nabiting such widely separated water-reservoirs as the Aral 

 Sea and Mississippi, or the Yang-tse-kiang and the continental 

 rivers of North America, must be representatives of very old 

 forms, remains of former fauna ; their having, at a mature age, 

 organs that do not serve them, but which merely remain as an 

 inheritance from former periods, is a confirmation of their sup- 

 posed antiquity— a conclusion drawn from zoogeographical 

 observations. 



The structure aud development of the dorsal shields, which, 

 in the case of Acipenseridse, spread all along the dorsal surface, 

 from the back edge of the head down to the dorsal fins, may 

 also, I think, help us to discern affinities between Ganoidei 

 Chondrostei and other fish. The first to pay attention to these 

 shields, and to suppose they were an embryonal dorsal fin, was 

 Prof. Zalensky. About the same time Prof Goethe described 

 a similar fin of a six-weeks-old sterlet, hinting, by the way, that 

 the dorsal shields might be compared with the dorsal rays of a 

 fossil fish, Coelacanthus, I have succeeded in investigating the 

 dorsal shields of a two-months-old sterlet, and in making a 

 whole series of cross sections, and I have arrived at the con- 

 clusion that Zalensky's and Goethe's suppositions are fully 

 established by facts. Indeed, between the shields spreads a 

 membrane, in which can be seen the same horny rays that are 

 generally seen in developing fins of fish ; right and left of 

 each dorsal shield there is a muscle, traces of which can also be 



found under the shields of grown sterlets. At last, having 

 made cross-sections of oxidized dorsal shields of grown sterlets, 

 a canal could be perceived in them. These canals are par- 

 ticularly well seen in Scaphirhynchus, as an older and a better 

 representative of the original type. 



Knowing that Dr. Giinther in his excellent book on ichthyo- 

 logy places the Acipenseridae and Cuelacanthi next to the 

 Polypteroidei, I availed myself of the offer of Prof. Bogdanoff, 

 Director of the Moscow Museum, and my teacher, to let me 

 examine the only dry specimen of I^lypter^is stnegalensis that 

 was in the Museum. Comparing the numerous small fins 

 spreading all along the back of Polypterus, there being a great 

 and wide front bone-ray, and the others being thin and horny, 

 I became convinced of their complete similarity to the dorsal 

 shields of a young sterlet and to the membranes which connect 

 them. 



In the wide bone-ray of Polypterus a ray channel could also 

 be discerned, and the rays of the membrane that spreads behind 

 the wide ray were also horny, like the rays of the membrane of 

 an embryonal fin of a sterlet. This brought me to the con- 

 clusion that the ancestors of both the AcipsnseridtB and the 

 Polypteroidei had not only a back fin, but also well developed 

 front dorsal fins, with great bone-rays and smaller horny rays, 

 and were, perhaps, nearer to each other than their present 

 descendants. 



A study of other organs, especially those in younj Acipen- 

 seridoe and Scaphirhynchus, convinces me that there is a closer 

 relationship between the Ganoidei Chondrostei and the Poly- 

 pteroidei than has hitherto been supposed. It is well known 

 that the conus arteriosus of Acipenser is distinguished from the 

 same organ of the Polypterus and Lepidosteus by a much 

 smaller number of transversal rows of valves. In young sterlets 

 I have found, besides developed valves, undeveloped folds lying 

 between the valves. In place of such undeveloped valves, in 

 the case of grown fish, as for example in a specimen oi Acipenser 

 huso which I dissected, and which was about 10 feet long, 

 an unevenness and roughness of surface are noticed. The air- 

 bladder, which in Lepidosteus and Polypterus partly resembles 

 the lung of Dipnoi, when attentively studied in the Acipenserida^ 

 does not appear to be so well adapted to its new functions. 

 Its coatings include many ramifications of vessels, the histological 

 structure of which is so similar to the structure of the coatings 

 of the digestive organs that it is much easier to recognize their 

 relative layers than in those of other fishes, where the air- 

 bladder is fully adapted to its functions. The ductus pneu- 

 maticus, in young sterlets especially, is very wide; a two- 

 months-old sterlet has it of almost the same width as an oeso- 

 phagus, and the food of the small fish, consisting mostly of 

 forms of Cladocera and Ostracoda, and also of statoblasts of 

 Polyzoa, especially Alcyonella, fills the cavity of the air-bladder 

 like the cavity of the stomach. 



Though the brain of these fishes has been well investigated, 

 yet in its organization one finds much that is interesting. For 

 example, the cerebral hemispheres of the prosencephalon of 

 Scaphirhynchus proved to be more similar to the hemispheres of 

 Dipnoi and Lepidosteus and Protopterus, than to th >se of Aci- 

 penser. The lateral layers are turned upward, so that the 

 upper portion of the hemispheres proved to consist, not of one 

 pallium, as in Acipenser, but also of the coating of the cere- 

 brum. The epiphysis cerebri, being a changeable organ, proved 

 to vary even in the limits of the genus Acipenser. Thus, its front 

 end in Acipenser sturio reached as far as the line connecting the 

 two lower nostrils, forming an angle of nearly 28" with the 

 surface of the brain, whereas in Acipenser ruthenus the epiphysis 

 forms an angle of almost 80°, and becomes a much shorter organ. 

 In some sterlets the end of the epiphysis cerebri went through 

 the cranium, and was only covered by the bone shields of the 

 exterior coating. Scaphirhynchus had the epiphysis less change- 

 able and more similar to the epiphysis of other Ganoidei and 

 Dipnoi. In other respects the brain of Scaphirhynchus also 

 proved to have a closer resemblance to the other Ganoidei than 

 to the Acipenser. Thus, its valvula cerebelli and lobi in- 

 feriores are more developed than those of a sterlet, and even 

 remind one of the brain of Amia and its near relatives Teleostei. 



Notwithstanding the scantiness of the facts stated here, I 

 indulge the hope that they may add something to the means at 

 our disposal for the settlement of the relationship between 

 Ganoidei Chondrostei and other Ganoidei. 



Nicholas Zograff. 



Moscow, 20/8 September 1878, 



