626 REPORT— 1902. 



progress greater, perhaps, than with the higher groups. Certainly is this the case 

 if, as to bulk, the literature in systematics and palaeontology be alone taken into 

 account. 



Of the Dipnoi our knowledge is fast becoming complete. "We know that 

 Lepidosireyi forms a burrow ; ^^ and, in consideration of a former monstrous proposal 

 to regard this animal, with its fifty-six pairs of ribs, and Profopterus, with its 

 thirty to ihirty-five, as varieties of a species,^'- it is the more interesting to find that 

 the Congo has lately yielded a Protoj}terus {P. dolloi) with the lepidosiren rib 

 formula, viz., fifty-four pairs. '^^ 



As a foremost result of American palaeontological research we have to record 

 the occurrence, in the Devonian of Ohio, of a series of colossal fishes known as the 

 Arthrodira, the supposed dipnoan affinities of which are still a matter of doubt.-* 



We have evidence that the osseous skeleton in a plate- like form first appeared 

 as a protection for the eye of a primitive shark."^ And coming to recent forms 

 having special bearings on the teachings of the rocks, we have to acknowledge 

 the capture in the Japanese seas of a couple of ancient sharks, of which one 

 ( Ch/ami/doselac/ais), since observed to have a distribution extending to the far North, 

 is a survivor from Devonian times ; the other (Mitsukurina), a genus whose gro- 

 tesqueness leaves no doubt of its identity with the Cretaceous lamnoid Scapayio- 

 rhyyichus.'^'' In the elucidation of the ISturiones and the determination of their 

 affinities with the ancient PaUieoniscidaj a master stroke has been achieved."" In 

 the Old Red genus Palceospondylus we have become familiar with an unmistakable 

 marsipobranch, possessing, as do certain living fishes, a notochord, annulated, but 

 not vertebrated in the strict sense of the term."^ The climax in Ichthyopalseon- 

 tology, however, has been reached, in the discovery of Silurian forms, which, there 

 is every reason to believe, explain in an unexpected way the hitherto anomalous 

 Pteras- and Cephalaspidians, by involving them in a community of ancestry with 

 the primitive Elasmobranchs. The genera Thelodus, Drepanaspis, Ateleaspis, 

 and Lanarkia, chief among these aunectant and ancestral forms, are among the 

 most remarkable vertebrate fossils known. ^'■' 



Passing to the Recent Fishes alone, the discovery which must take precedence 

 is that of the mode of origin of the skeletogenous tissue of their vertebral column. 

 The fishes, unlike all the higher Yertebrata, have, when young, a notochord invested 

 in a double sheath, there being an inner chordal sheath, an outer cuticular, which 

 latter is alone present in all the higher groups. The skeletogenous cells, by whose 

 activity the cartilaginous vertebral skeleton is formed, arise outside these sheaths ; 

 but whereas, when proliferating, they in one series remain outside, they in the 

 other, by the rupture of the cuticular sheath, invade the chordal. This distinction 

 enables us to discriminate between a Chordal series, which embraces the Chimse- 

 roids, Elasmobranchs, and Dipnoi, and a Perichordal, consisting of the Teleosts, 

 Ganoids, and Cyclostomes.''" 



In consideration of the enormity of the structural gap between the cyclostomes 

 and the higher Vertebrata this is an extraordinary result. For be it remembered 

 that, in addition to their well-known characters, the lampreys and hags (1) in 

 the total absence of paired fins; (2) in the presence of branchiae, ordinarily seven in 

 number, fourteen in Bdellostoma polytrenial'^ numerically variable in individuals 

 of certain species between six and fourteen, and doubtfully asserted in the young 

 of one to be originally thirty-five ; "'- and (.3) in the carrying up of their oral hypo- 

 pophysis by the nasal organ, whereby it perforates the cranium from above, as 

 contrasted with all the higher Vertebrata, in which, carried in with the mouth-sac, 

 it perforates it from beneath, exhibit morphological characters of an extra- 

 ordinary kind. And if we are to express these characters in terms, we may dis- 

 tinguish the Cyclostomes as apterygial and epicraniate, the higher Yertebrata as 

 hypocraniate?'^ ^ But this notwithstanding, the aforementioned subdivision of the 



' It is an interesting circumstance, if their ' ciliated sac ' is rightly homologised, 

 that Amphioxiis and the Tunicata present a corresponding dissimilaritj', allowance 

 being made for the fact that in Botryllus, Goodsiria, and Polycarpa the sac overlies 

 the ganglion.'* It is pertinent here to recall the ammocoete-like condition of the 

 ' endostyle ' in Oilwpleura, JiabellurA?'" 



