( 223 ) 



(lots of the "Schhisslcistcn". The cell houiidai'los eaniiol he followed 

 HOW fcom one side of (he wall (o Ihe olhei'; al (he basal side of (he 

 cells, there where the (ihi-illae are formed, the cell inembraneö have 

 disappeared and the protoplasm of the cells is continnons. It seemed 

 to me that the disappearance of the cell limits preceded the differen- 

 tiation of the mjoübrillae, on the olher hand the question arises, 

 whetJier the differentiation of the fibrillae does not give the impulse 

 for the disappearance of the cell membranes. For in stu'djing these 

 cells closer, we sometimes find in cells, where on\y at the basal side 

 of the cell the cellular membranes have disappeared, fibrillae lying 

 there where the cells are still distinctlj separated. These fibrillae do 

 not pass from one cell to another, but end close to the cell-membrane 

 with a small thickened point (fig. 3), and sometimes in two adjoining 

 cells a pair of such lil)i"illae are seen just opposite to each other. 

 In following stages of development in this part of the cells a gi-eater 

 number of fibrillae is to be found; these fibrillae then are seeji to 

 pass through different cells and the membranes of the cells have 

 disappeared here too. These facts remind us of the appearance of the 

 fibrillae on the boundaries of the myotomes (in longitudinal sections), 

 and this being the beginning of the fusion of the fibrillae of the 

 adjoining myotomes, the question arises, whether a similar process 

 is going on in the heart muscle cells. Be this as it may, the fact 

 remains, that only at that side of the cell in which the myofibrillae 

 are formed, the membranes disappear and the protoplasma fuses. 



We may call attention here to the fact, that the black meshes and 

 lines of the "Schlussleiste" have disappeared at the basal side of the 

 cells, there wliere the cell limits ceased to exist; at the of her side 

 of the cells, there where the cells are still shar|)ly se[)ara(ed, they 

 remain as clear and distinct as before. 



In fig. 4 one half of a cross section (hrough (he Iiear( (ube is 

 drawji, to demonsfrafe once more the course of the fibrillae and the 

 sfrucfure of the myocard cells. 



In (he figure we see the endocardium (end.) composed of fiattened 

 cells, and around it the myocard^). The fibrillae are here cut length- 

 wise, and may bo followed without break through different cells. 

 The cellular limits, seen in the outer half of the cell-body and absent 

 in the inner half, we need not (lescrif)e at length any more. 



In preparations in which the centrosomes are stained in the other 

 embryonic cells, in some cells of the myocard too they were ^•isible 



1) A pericai'dial membianc as a covering of llie myocard, as il sliows itself in 

 .sahnons during Ihc later stages of development, is not yet developed lici-c. 'flie 

 heart lies enliroly free inside the p(M'ienrdial cavily. 



