DEVELOPMENT OF DISCS, HEART MUSCLE OF PIG 337 
There is some doubt here, whether this statement refers to the 
embryo four days after conception or to the animal four days 
after birth. 
The lower vertebrates presented dises which were much less 
numerous and complex as the animals went down the scale of 
complexity. ‘These discs presented no evidence in favor of the 
cell-boundary theory, since they were superficial in position, 
often lay over a nucleus, were situated at random with 
relation to the nucleus, and did not appear earlier than the 
striations. They seemed to be a part of, or closely related to, 
the anisotropic lines, since they shaded into these and were 
parallel to them in all cases. 
H. E. Jordan and J. B. Banks’ in 1917 worked out a study of 
the intercalated discs in the heart of the beef. In this paper 
the fetal heart was used after a study of the adult heart had been 
completed. The youngest fetal heart was one of approximately 
two and one-half or three months of age. In this, the cells were 
found to be fusiform, showing some signs of anastomosing later- 
ally and terminally. Slight striations were visible and the 
intercalated discs appeared as large dots, shading into the tel- 
ophragma. They were situated at random in the cells, but did 
not occur at the point of terminal fusion of two cells. None of 
them were more than peripheral. With the increasing age of 
the embryo, the discs became more distinct and more complex 
until in the adult heart they took the form of step-like formations 
very much complicated in structure. 
No investigator, as far as I have been able to find, has taken 
up the study of fetal heart tissue in any animal with the thought 
of especial investigation as to the time of appearance of the discs, 
their development, and their function. Whatever work has 
been done on fetal material concerning the discs has been more 
or less superficial, rather than very detailed. 
DESCRIPTION 
In this description the early stages of the series of pig embryos 
will be considered briefly with regard to the histogenesis of heart 
muscle. The later stages will be considered more in detail 
since they show the origin and development of the discs. 
