DEVELOPMENT OF THE SKELETON OF THE TUATARA. 7 



3. METHODS AND RECONSTRUCTION. 



Methods. Dissection was resorted to only in the later stages, and wherever the 

 elements under consideration were fully formed. Throughout the earlier stages, and 

 in the later where necessary, microscopic sections were relied upon ; and further, as 

 for example at Stage S and in dealing with the carpus and tarsus, dissection was duly 

 checked by section, as a means of ensuring accuracy of detail. 



The microscopic sections were in all cases mounted serially, the plane of section 

 being determined by the object in view (as set forth in the accompanying description 

 of the Plates). After preliminary experiment with the Green Lizard (Lacerta viridis), 

 it was found that diiferentiation of the skeletogenous tissues could best be obtained 

 by staining in bulk with Ehrlich's haematoxylin, and afterwards on the slide with 

 Griibler's orange G. For this suggestion and much subsequent aid we are indebted 

 to Mr. M. F. Woodward, Demonstrator of Zoology, Royal College of Science, London, 

 than whom no better manipulator or master of micro-chemical technique exists ; and 

 we found, as our work proceeded, that much time is to be saved by dissolving the 

 orange in 70 p. c. alcohol, with the addition of a few drops of glacial acetic acid, 

 thus eliminating the tedium arising out of the use of a mere aqueous solution. The 

 results of this method are exceedingly satisfactory, cartilage being as a rule differen- 

 tiated blue, bone in all its forms deep yellow, while the other tissues behave each in 

 its own way. 



Reconstruction. Since the time has no r .v arrived at which mere dissection is 

 insufficient for the study of the facts of skeletogenesis, recourse was had to the 

 so-called Bornean method of reconstruction from microscopic sections 1 . We were 

 under the necessity of working with thin plates, and found that if made of the 

 Bornean mixture of beeswax and turpentine there was difficulty in preparation and 

 liability to snap. By substituting vaseline for turpentine, we entirely overcame all 

 this, and we can confidently recommend our mixture as reliable. 



The figures which constitute PL III. and figs. 7 and 10 of PI. VI. are all from 

 models prepared from plates thus made. For the most part the sections of the animal 

 were cut to a uniform thickness of 10 /u, and each plate made to that of 1 millim. 

 Tracings were then drawn upon the plates, by means of the camera lucida, of sections 

 at regular intervals, determined by the degree of magnification (every fourth section 

 for a magnification of 25, every third for that of 33, and so on). In cutting out the 

 tracings, trabecula? were left where necessary for holding the parts together during 

 reconstruction, and afterwards cut away. For the process of cutting, the best results 

 were obtained by the use of a needle, the plates being laid upon glass. 



1 Earlier achievement in the same direction must not be overlooked. In England it stands memorably 

 associated with the Huxleyean traditions: c/.E. T. Newton, " On a New Method of Preparing a Dissected Model 

 of an Insect's Brain from Microscopic Sections,'' Journ. Quekett Microscop. Club (I.), vol. v. 1878, p. 150, and 

 Qu. Journ. Micr. Sci. (u. s.) vol. six. p. 340. 



