714 SUMMARY OF CURRENT RESEARCHES RELATING TO 



pigment seems to be exogenous not " autochthonous," for the young trout 

 show clearly an invasion of the epidermis from the cutis. As to the 

 chemical nature of the pigments, Krukenberg's results are corroborated. 



Resistance of Gasterosteus aculeatus to the Osmotic Pressure of 

 different Media.* — M. Siedlecki has subjected specimens of G. aculeatus 

 to solutions in varipus degrees of concentration of sugar, glycerine, potas- 

 sium chloride, sodium chloride, sodium sulphate, &c, and finds that they 

 show resistance to a high degree of osmotic pressure. He considers 

 that the epithelium of the body and gills acts as a semipermeable membrane 

 to certain substances ; when the epithelial layer is partly disintegrated 

 the resistance is so diminished that the animals succumb rapidly even in 

 weak solutions. 



Gill-Filters of Freshwater Fishes.t — Enoch Zander gives a careful 

 account of the " sieve-processes " which occur on the edges, or only on 

 the anterior edge of the branchial arches. They differ greatly in form, 

 number and disposition, and Zander connects the manifold arrange- 

 ments with the nature of the food. In predatory fishes, like pike and 

 burbot, the sieve-processes are absent or very primitive, while the cavity 

 of the mouth and pharynx bears pointed teeth for gripping the prey ; 

 but fishes which feed on small organisms, which grub in the mud, 

 and so on, have a fine filter between the gill-clefts. In general, Zander's 

 results agree with what Arnold has noted in regard to the same subject, 

 but the detailed illustrations are of much interest. 



Palaeospondylus.J — "W. J. Sollas and Igerna B. J. Sollas have investi- 

 gated this fossil by means of serial sections, showing that the substance 

 of which the fossil consists is a true coal. " The organism was evidently 

 a primitive fish, with some features which are suggestive of Marsipo- 

 branchs, some of Elasmobranchs, and some of young Dipnoi or larval 

 Amphibians ; after branching off from the Piscine stem, at a point below 

 the origin of the Elasmobranchs, it pursued an independent course of 

 development." 



Appendages ofTremataspis.§ — W. Patten concludes a detailed argu- 

 ment with the statement that we are justified in crediting Tremataspis 

 with a pair of oar-like swimming appendages — probably attached to the 

 largest pair of incisions on the anterior ventral margin of the head — 

 similar to those of Bothriolepis and Pterkhtkys. Similar appendages 

 were probably present in Pteraspis, Cyathaspis and Tolypaspis. 



That by far the greater share of the Avork of locomotion in the 

 Ostracoderrns must have been performed by the oar-like cephalic 

 appendages, is indicated by their anterior position and great size in 

 Bothriolepis and Pterkhtkys, and by the relatively small size of dorsal 

 and caudal fins in the latter genus. Such a condition is in marked 

 contrast to that in many of the most primitive of the true fishes, where 



* Comptes Rendus, cxxxvii. pp. 469-71. 



f Zeitgchr. Wiss. Zool., lxxv. (1903) pp. 233-f>7 (17 figs.). 



j Proc. Roy. Soc, London, lxxii. (1903) pp. 98-9. 



§ Anier. Naturalist, xxxvii. (1903) pp. 223-42 (9 figs.). 





