308 SUMMARY OF CURRENT RESEARCHES RELATING TO 



elsewhere) is in proportion to the relation between the total surface of 

 tho body in contact with the external medium and the volume of the 



body. 



Prof. E. Perrier * criticises some of Fruvot's interpretations involved 

 in the paper above referred to. Pruvot traces back stolonisation in 

 Syllids to the phenomena of epigamy or epitoky ; Perrier points, how- 

 ever, to the fresh-water Naidcinorpha where stolonisation is conspicuous 

 without any trace of epigamy. Moreover, stolonisation is associated 

 with the non-sexual periods in Nais, Dero, &c. It should be traced 

 back to tho posterior budding which is the characteristic mode of growth 

 in Annelids. 



Pruvot regarded stolonial reproduction as a recent acquisition, 

 mainly because of the diversity in its modes of occurrence even within 

 one genus ; Perrier argues that the more legitimate inference is that 

 stolonisation is a survival of primitive conditions. Perrier also refuses 

 to accept Pruvot's " laws," which do not agree with what may be observed 

 in Myrianida for instance. Sounder generalisations are to be found in 

 Geofi'roy Saint-Hilaire's " balancing of organs," and in Perrier's general 

 theory of the formation of the Annelid body by posterior budding (Les 

 Colonies Animates, 1881). 



Alimentary Canal of Lagis koreni.f — L. Brasil describes the general 

 structure of the gut in this Pectinarian and discusses the regeneration of 

 tho intestinal epithelium. Nuclei migrate towards the surface, exhibit 

 mitoses, and then migrate back towards the base. The same was seen 

 in three other Polychsets and has been described by Heymons in the 

 embryo of Scolopendra. 



Nematohelminth.es. 



Cystoopsis acipenseri4 — W. Zykoff confirms Wagner's description 

 of this interesting nematode which occurs beneath the skin of Acipenser 

 ruthenus in guinea-worm fashion. The minute male is found along with 

 the female in the same tubercle. This opens eventually like a boil, and 

 the thread-like uterus full of embryos is extruded into the water. Zykoff 

 gives some reasons for supposing that the intermediate host is Simulia 

 rcptans, on wbich the sterlet is wont to feed. 



Platyhelminthes. 



Distribution of Planarians as affected by Temperature.§ — Prof. 

 W. Voigt has made, as formerly reported, a detailed study of the dis- 

 tribution of Planarians in Alpine streams. He now corsiders tho causes 

 of the cdimination of Planar ia alpha in the " Hundruckgebirge" and of 

 Polycelis cornuta. His argument rests on the results of laborious collect- 

 ing and temperature-observations, and does not admit of brief summary, 

 but the outcome shows that Planaria alpina, PL gonocepliala, and Pol. 

 cornuta are very sensitive to temperature-changes, such as those which 

 ensue in tho streams as the result of de-foresting. 



New Trematodes from Crocodile.||— Th. Odhner found in the intes- 

 tine of the Nile crocodile a new species of tho interesting Holostomid 



* Tom. cit., pp. 453-6. 



t Arch. Zool. Expe'r.. x. (1901) Notes et Revue, pp. i.-iv. (6 figs.). 

 t Biol. ( enfiulbl., xxii. (19(12) pp. 229-33 (2 fi»s.). 



§ Verb. Nat. Ver. Rheinland, lviii. (1901) pp. 225-46, 1 pi. (map), 2 figs. (maps). 

 || Ofvertigt k. Vetensk. Akad. Forl.andl.. lix. (1902) pp. 19-45 (3 figs.). 



