The Histogenesis of Cysticercus pisiformis. 219 



X, is shown. This latter cell I consider as the neuron; the others 

 which correspond, roughly at least, with those shown in the above- 

 mentioned figures of Tower are probably parenchyma cells. The 

 staining of the slide from which this drawing was made was not 

 such, however, as to permit of any definite conclusions on this point. 

 It is to be further noted that in Tower's figures no essential 

 difference exists between his "binding cells" and "ganglion cells" 

 (compare his figs. 15 and 16 for example). 



The fact has already been mentioned that distinct polarity is 

 lacking in many of the embryonic ganglion cells, but uni-, bi- and 

 multipolar cells occur. The neurons of the cords and their per- 

 ipheral branches are, as has already been stated, typically bi-polar. 

 Occasionally uni-polar neurons are found, but such cells are probablj^ 

 in reality bi-polar, their single process branching T-shaped within 

 the cord. 



CoHx (1898) has stated that the "ganglion" cells are all 

 approximately of one size, in which connection he takes occasion to 

 criticize Laxg (1881) and others who have described difterences in 

 size of the neurons. Actual measurement of these ceUs is obviously 

 very difficult, since, as Cohx points out, the plane in which the cells 

 are viewed alters their apparent form and size very materiallj'; and 

 moreover, since the cells have no definite termination but merge 

 insensibly into their processes, it will depend entirely on the judgment 

 of the individual investigator what length the cell shall receive. 

 This last difficulty is largely obviated if the nucleus be chosen for 

 comparison, but even here the plane of observation is liable to affect 

 the results, and the accurate measurement of such comparatively 

 small objects is not readily accomplished. Further, since former 

 observers have usually chosen the cells for measurement, measure- 

 ments of the nucleus alone are not satisfactory for purposes of 

 comparison. 



No measurements of the peripheral neurons have been made. 

 If the reader will, however, compare Figs. 50, 56, 58 and 59, he can 

 readily satisfy himself that marked differences, not only in position, 

 but also in size and shape, are shown by the neuro-muscular cells. 

 The variations occurring in neurons of the peripheral system, other 

 than the neuro-muscular cells, I have not investigated. 



The following are the measurements^) of 12 neurons from the 



1) All measurements following are in micra. 



