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RANDOLPH. [Vol. VII. 



long and careful work upon all stages of development gave no 

 clue to the solution of the problem, and it was only after the 

 discovery of the process in Lumbriculus that I could trace in 

 Lumbricus an apparent agreement. Since that time I have 

 also carefully examined the mode of regeneration in Tubifex 

 and the budding of Nais elinguis and Chaetogaster. It is abso- 

 lutely necessary, in order to gain a thorough insight into the 

 growth of any of these forms, to study specimens of many 

 stages. Although in regeneration there is a progressive devel- 

 opment, and the new mesoderm of the anal segment retains its 

 embryonic condition to a certain extent for a considerable time, 

 its most striking stages are passed through during the first and 

 second days (neoblasts and circular muscles). By the time that 

 the anterior region of the new tail is differentiated, the most 

 posterior part has long passed through its initial phases. This 

 seems the more worthy of remark, since it is probable that one 

 cause contributing to the misconception of Btilow, as to the 

 origin of the new mesoderm, was the attempt to trace the whole 

 process in the same series of sections. 



I gladly avail myself of this opportunity to acknowledge my 

 great indebtedness to Professor E. B. Wilson, under whose di- 

 rection in the biological laboratory of Bryn Mawr College this 

 work was carried on nearly to completion. It was finished in 

 the zoological laboratory of the University of Zurich, and for 

 the interest that Professor Lang has shown in my work I am 

 very grateful. 



Methods. — The methods that were found to give the most 

 satisfaction were : — 



For Preserving and Hardening. — Perenyi's fluid, one to two 

 hours ; alcohol, 70 per cent, one hour, followed by 90 per cent. 



For Staining. — Borax carmine, acid alcohol a few minutes 

 subsequently neutralized by very weak ammoniacal alcohol, and 

 Kleinenberg's haematoxylin. 



For the Study of the Development of the Muscles. — Borax 

 carmine, followed after the sections were fastened to the slide 

 by picric acid dissolved in 70 per cent alcohol. 



Corrosive sublimate and chrom-acetic acid were used without 

 as great success, and no single staining gave such clear and defi- 

 nite results as the double staining described. 



