No. 441.] NOTES AND LITERATURE. 



should be abandoned together with the insufficient neurone theory, 

 and facts concerning the neurofibrillar should be sought. This in 

 general is Nissl's position and it will probably carry to the mind of 

 the neuronist the conviction that if this is a fair example of what the 

 neurone theory will have to meet, that theory is still very safe. 



Notes. — The earliest stages in the development of the teeth in 

 selachians have been investigated by Laaser {Jena. Zeitschr.f. Natur- 

 wissench, Bd. 37, pp. 551-578), who finds that in embryos of Spinax, 

 Acanthias, and Mustelus of three to four centimetres in length, a den- 

 tal ridge is formed by a thickening of the epithelium of the jaws. 

 The ridges are formed earlier in the lower jaws of Spinax and Acan- 

 thias and in the upper jaw of Mustelus. Teeth develop not only in 

 the dental ridges but also in the adjacent epithelium where in their 

 early stages they are indistinguishable from placoid scales. The 

 first hard part formed is the dentine, the enamel being entirely absent 



Professor Bastian (London, Williams & Margate. Ft. II. 1902, 

 pp. 63-147, pis.) presents in a second installment much additional 

 evidence in favor of his views on heterogenesis. Thus he believes 

 he has shown that vorticellae may be produced from a pellicle largely 

 composed of spirilla, that amoebae may be made to segment and 

 their parts be converted into ciliate infusoria, that the entire egg of 

 the rotifer Hydatina can be transformed into a ciliate infusorian 

 Otostoma, etc. The paper is illustrated by photographic reproduc- 

 tions but even these cannot shake the conviction of many zoologists, 

 that because of the methods used something is probably wrong with 

 the observations recorded in the text. 



Dr. J. Anglas has published as number 17 of the biological series 

 of " Scientia " a clear account of the changes undergone by the tis- 

 sues during the internal metamorphosis of insects. The histogenesis 

 of early development is first taken up, then the process of histolysis, 

 and finally the reconstructive processes. The book contains a final 



The origin and classification of leucocytes and a very readable 

 discussion of the theories of their relations to health and disease 



