NERVUS TERMINALIS: TURTLE 435 



which were spherical or nearly so. In the case of some cells, 

 especially many in the terminalis ganglia, the nuclei were so 

 elongated that it was necessary to measure the greater and the 

 lesser diameters and take the mean of the two. 



All of the measurements and the drawings of the ganglion cells 

 represented were made from a single embryo of 10-mm. carapace 

 length, stained with iron-hematoxylin. This was done for the 

 sake of uniformity, although the statements hold in general for 

 all the embryos examined which were sufficiently advanced to 

 show any pronounced differentiation of the various types of nerve 

 cells. In drawing the figures the outlines of the cells and nuclei 

 were traced with the aid of the camera lucida, and the same com- 

 bination of lenses was employed in each case, so that the figures 

 represent directly the variations in form and size of the various 

 types. 



Comparison of embryos at different stages of development in- 

 dicated that in embryos of 10-mm. total length, the spinal gan- 

 glion cells were on the average somewhat larger than those of 

 the sympathetic chain ganglia. There was, however, but slight 

 difference in the size of the individual cells within the spinal 

 ganglia. The sympathetic chain ganglion cells had stiU much 

 the appearance of indifferent cells. In the gasserian ganglion of 

 embryos at this stage of development, many of the ceUs were 

 larger than the spinal ganglion cells of the same embryo. 



In embryos of 9.5 to 11-mm. carapace (15.5 to 17 mm. greatest 

 length) there is a marked difference between the size of the 

 largest sensory ganglion cells and those of the sympathetic 

 chain ganglia. The latter (fig. 12) are of pretty uniform size, 

 but the spinal ganglia and, in less marked degree, the cranial 

 ganglia, showed two fairly distinct sizes of cells. The larger 

 type in the spinal ganglia (fig. 9) was found near the periphery 

 of the ganglion. Many had already reached the unipolar con- 

 dition, but others showed various transitional stages from the 

 primitive bipolar cells. 



Of one hundred cells measured from three different ganglia, 

 one in the thoracic region, one in the lumbar, and one in the 

 sacral, the largest nucleus had a diameter of 12.3 m and the 



