THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol.. XV. MAY, 1894. No. 5. 



A Method for Orienting Small Objects for the Microtome.* 



By W. McM. WOODWORTH, 



CAMBRIDGE, MASS. 



In studying tlie embryology of Polychcerus caudata, an 

 acoelous Turbellarian, I experienced great difficulty in 

 obtaining sections in definite planes, owing to the ex- 

 treme smallness and nearly spherical form of the early 

 stages. The difficulty lay in controlling the plane of sec- 

 tion in relation to the axes of the object. The embryos 

 measure only about 0.224 mm. in diameter, and all orien- 

 tation must be done under low powers of the microscope. 

 I tried orienting in paraffin, which was kept fluid by 

 means of hot water circulating through a combination 

 Strieker's gas and warm stage into the central well of 

 which iced water could be quickly introduced. I hoped 

 thus by the sudden cooling of the paraffin to fix the ob- 

 ject in the position into which it had been brought by 

 means of needles. This method proved useless, for ow- 

 ing to their lightness and spherical shape the objects 

 could not be kept long enough in one position, being 

 moved about by the convection currents in the hot par- 

 affin. The method suggested by Born (Zeitschr. f. wiss. 

 Mikr., Bd. V. p. 436, 1888) was also tried, but was not 

 applicable to objects so small and round, it being impos- 

 sible, in early stages, to determine the position of the 

 poles of the egg owing to the fact that the grooves of 



*From Bull. Comp. Zool., Harvard College, XXV, 3. 

 To orient : To define the position of. — Webster. 



