546 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Homology of Selachian Ampullae.* — J. B. Johnston differs entirely 

 from the argument of Allis that the nerve-sacs of Ganoids and the 

 ampulla? of Selachians are the homologues of the end-buds of Teleosts, 

 rather than of the lateral line or pit-organs. He criticises the bases of 

 the arguments which Allis advanced, and emphasises the constancy 

 of the cLief divisions of the nervous system, and the inseparable and 

 unchangeable unity of the central and peripheral elements of each 

 functional division. 



Homologue of Infundibular Organ in Amphioxus.f — J. Boeke 

 finds on the ventral wall of the cerebral ventricle of the larval lancelet 

 (l'5-4"8 cm. in length), at a definite spot, a well-defined organ-like 

 differentiated portion of the ventricle-epithelium, which he regards as 

 the homologue of the infundibular organ in higher Chordates. The 

 infundibular organ would thus be older than the infundibular evagina- 

 tion, which appears contemporaneously with the brain-curvatures. 



Note on Additions to Fresh-water Fauna.} — C. Vaney and A 

 Conte report the appearance in the fresh water of Lyons of Emea 

 lacustris or Tetrastemma lacustre, — a Nemerteau discovered by du Plessis 

 on the Savoy side of Lake Geneva. It exhibits a natural scissiparity. 



Another recent addition to the Lyons fauna is Blennius atycstris, 

 first found by Blanchard in the Lake of Buurget. Like Emea, it has 

 probably reached Lyons via the Khone. 



The authors go on to discuss the adaptability of various fishes to 

 change of habitat ; thus Blennius pavo and Gobius niger can stand abrupt 

 change to fresh water, sticklebacks require more gradual transition,, 

 while Crenilabrus masso is at once killed if taken from the shore and 

 put into fresh water. There seems no doubt that Blennius alpestris is 

 a variety of Bl. cagnota, adapted long ago to a fresh-water habitat. 



Fossil Faunas and Geological Formations. § — H. S. Williams- 

 submits a series of statistics from which he deduces the following 

 " laws." 



A geological fauna may be defined as an aggregation of species 

 living together, the several species of which hold a definite value in 

 relation to each other. 



The relative value of the constituent species is expressed in terms, 

 of the abundance or rarity of the individuals of each faunal (" faunule ") 

 sample, viz. bionic value. 



The purity or integrity of the fauna may be recognised by the list 

 of its dominant species. The geographical distribution of the fauna may 

 be recognised by the presence of the dominant species and their holding, 

 their standard dominance in the list of species with which they are asso- 

 ciated in the " faunule." The region, over which the bionic equilibrium 

 of the faui a is expressed by occurrence of the same dominant species,, 

 is the metropolis of the fauna. The geological range of a fauna is 

 recognised by the persistence of the bionic equilibrium of the species. 



Two faunas may coexist in time in distinct geographical areas ; but 

 in the same area, the two faunas can appear in their integrity only by 



* Anat. Anzeig., xxi. (1902) pp. 308-13. t Tom. cit, pp. 411-4 (3. figs.). 

 % Comptes Rendus, exxxiv. (1902) pp. 115-7. 

 § Ainer. Journ. Sci , xiii. (1902) pp. 417-32. 



