570 SUMMARY OF CURRENT RESEARCHES RELATING TO 



seen in mammalian blood cannot be applied to fisbes. An explanation 

 cannot be looked for nntil tbe blood-forming organs have been studied. 



Cerebellum of Petromyzon.* — Prof. Alfred Schaper points out that 

 the slightly developed cerebellum of the lamprey has always been 

 regarded as of the nature of a commissure only, and therefore has been 

 tacitly supposed to consist only of nerve-fibrils. He has however found 

 that not only are numerous cellular elements present, but that tbey are 

 arranged in layers generally corresponding to those of other vertebrates, 

 especially amphibians. The superficial layer shows the general charac- 

 ters of the molecular layer. Beneath lies a layer of cells corresponding 

 to Purkinje's cells, and a well-defined granular layer. As in amphibians 

 the medullary layer is absent. Generally there is clear evidence that 

 the cerebellum of Petromyzon, though much reduced, is the homologue 

 of that of other vertebrates — a point of some importance in connection 

 with the phylogeny of the vertebrate brain. 



c. G-eneral. 



Animal Mechanics.! — Dr. Otto Thilo further elaborates his pre- 

 vious statements as to the part played by check action in the mechanics 

 of organisms. Where any part of the body has to be long maintained 

 in one position, the muscular strain would be very severe, were it not 

 lightened by the construction of the hard parts, which are so arranged 

 as to prevent reversal of the action. Thus the spines of the dorsal fin 

 of Zeus faber exemplify the mechanical construction known as a ratchet. 

 In the dorsal spine of Monacanthus, a contact check is well illustrated, 

 while the adjustments of the fangs of a viper show another form of the 

 same mechanism. In general, the author is of opinion that check action 

 plays as important a part in animal mechanics as it does in the machines 

 constructed by man. 



Origin of Life.$ — Ludwig Zehnder, as a continuation of his volume 

 on ' The Mechanics of the Universe,' has published a book whose object 

 is to explain the organic world on mechanical principles. Beginning 

 with the atoms, the author evolves the phenomena of aggregation and 

 the forces of magnetism and electricity, and derives also his mechanical 

 bases. From the constitution of molecules, the author deduces his first 

 fundamental biogenetic law, which reads, " Substance struggles to repro- 

 duce itself." Each molecule seeks to generate new similar molecules, 

 and the new formed molecules are subjected to a process of selection, a 

 struggle for existence, which is identical for aggregates of molecules, 

 simple molecular structures, protists, plants, and animals. In conse- 

 quence the second fundamental biogenetic law may be formulated as 

 follows, " Substance seeks to adapt itself to the conditions of existence." 

 Organisms are conceived of as consisting of fistellae, or circular aggre- 

 gates of molecules. Spontaueous generation of such aggregates is theo- 

 retically possible, but improbable, and the improbability increases with 



* Anat. Anzeig., xvi. (1899) pp. 439-46 (4 figs.). 



t Biol. Central!)]., xx. (190n) pp. 452-61 (7 rigs.). Cf. this Journal, 1S99, p. 583. 



% ' Die Entstehung des Lehen.s, aus meclianischen Grundlagen entwickclt,' 1st 

 part, Freiburg, Leipzig, and Tubingen, 1899, 8vo, viii. and 256 pp. and 123 tigs. See 

 Bot. Centralbl., lxxxii. (191X0 P- 375. 



