582 SUMMARY OF CURRENT RESEARCHES RELATING TO 



By an involuntary migration, animals arc carried away by fish, 

 c. g. as eggs, or as fish parasites, &c. Though rare, landslips on the 

 shore may be a means which should be considered. 



Ebb tides carry mud from the littoral zone, and with this mud 

 eggs and small animals. 



Lastly, animals and eggs fix themselves to pieces of wood, &c, 

 which float away from shore, become waterlogged and sink, and the 

 animals may in this way become naturalized to a deep-sea life. If 

 these small causes, occurring year after year, be considered in the 

 aggregate, voluntary and involuntary migrations will probably bo 

 sufficient to explain the origin of this deep-lake fauna. 



B. INVERTEBRATA. 

 Horizontal and Vertical Geographical Distribution of the Pelagic 

 Fauna of Fresh-water Lakes.* — Dr. 0. E. Imhof finds that somo 

 species of Copepoda, Cladocera, Rotatoria, and Protozoa are ubiquitous, 

 while others are limited to very definite areas. This, which is par- 

 ticularly true of horizontal distribution, applies also to the vertical ; 

 Anureea longispina is the most widely distributed vertically, while 

 other species are found only at certain depths. 



Endothelium of the Internal Wall of Vessels of Invertebrates. f 

 M. W. Vignal finds that the vessels of invertebrates have an epi- 

 thelial layer which presents the same characters as the endothelium 

 of the lymphatics of vertebrates, and that the vessels of invertebrates 

 open into the interstices of the connective fibres, where, as we know, 

 Bichat and Ranvier place the origin of the lymphatics of vertebrates ; 

 this mode of origin is, in the author's opinion, more than probable, 

 although it has not been absolutely proved in consequence of the 

 obstacles to injections which are presented by the valves of the 

 lymphatic trunks. 



M. Vignal reminds us that Prof. Sabatier has noted the existence 

 of an endothelium on the internal surface of the vessels of the mussel, 

 but he has figured it as resembling a blood endothelium, while the 

 stomata which he figures are, as Afferow has demonstrated, due to 

 imperfect impregnation ; nor are they nuclei, as Sabatier supposes. 



Blood of Limulus, Callinectes, and a Holothurian.J — Dr. W. H. 

 Howell thinks that there is no good reason why there should not 

 exist to a certain extent, in closely allied animals having the same 

 general habits of life, a fundamental similarity in the chemical 

 constitution of the blood. An albumen may still be present in the 

 blood of an animal, as a remnant of a previous mode of life, although 

 now no longer useful ; and in this way the study of the blood may be 

 a useful indication of the true affinities of the animal. By the study 

 of the coagulation of the blood in the lower animals, since it is 

 probably simpler than in vertebrates, a better understanding of the 

 phenomena in mammalian blood may be obtained. 



* Zool. Anzeig., ix. (1886) pp. 335-8. 

 t Comptes Rendus, cii. (188G) pp. 102V8. 



% Stud. Biol. Laborat. Johns-Hopkins Univ., iii. (1886) pp. 267-87 (I pi.). 

 See also this Journal, ante, p. 68. 



