Irving Hardest Y 231 



chymal cells. Here is a syncytium with its nuclei variously distributed 

 and with a shape and boundaries none other than those of the entire 

 body of the animal itself. 



As to the processes by which the syncytium may be formed, His, 98, 

 in his paper " Ueler Zellen und Syncytienbildung/' states that a syn- 

 cytium may occur either in consequence of delayed formation of the cell 

 membranes or it may, secondarily, arise from a fusion of cells already 

 formed. In the first case the syncytium may or may not disappear 

 through a later formation of cell boundaries. Mall's description of the 

 connective-tissue syncytium deals with embryos in relatively late stages 

 and, in this case, it is needless to state that it maintains. It is a stage 

 in the development of a tissue, the very nature of which forbids its 

 breaking up into individual cells. Portions of the substance of the 

 syncytium may become converted or differentiated into structures differ- 

 ently arranged and chemically different from the remaining portion. 

 Fibrillse are developed in the muscle cell, and IMall has descrilDed the 

 development of different forms of connective tissue (fibrous, etc.) from 

 the s}Ticytial protoplasm. 



Material and Methods. 



Pig material has been used almost exclusively because the different 

 stages required could be more easily obtained. The observations have 

 been confined to conditions found in the spinal cord alone and in all 

 cases the pieces were taken from the cervical region. Preparations of 

 the adult pig were supplemented with similar preparations of human 

 spinal cord and with that of the ox. In order to follow the developmental 

 changes as closely as possible, preparations were made from quite a 

 number of pig embryos and foetuses. The smallest I was able to obtain 

 measured 5 millimeters, unflexed. Beginning with this, the series 

 involved about twenty different stages, the first seven being taken at 

 much closer intervals than the remainder. The series terminated with 

 a foetus of 28 centimeters, suckling pigs of two weeks, and specimens 

 from two adult hogs. Up to 10 millimeters the measurements could 

 be taken from head to tail ; after that " crown rump " measurements 

 were taken in the usual manner. 



During, and for a time after, the flexion of the embryo, measure- 

 ment is a very imsatisfactory method of expressing age in pigs. A 

 flexed embryo may measure only 7 millimeters, when an unflexed, and 

 evidently younger one, may measure 8 millimeters. Also from 15 to 

 30 millimeters, pigs giving the same crown rump measurement may 



