116 CARNEGIE INSTITUTION OF WASHINGTON. 



form to another. A single initochondrium may bend back and forth 

 with a somewhat undulatory movement, or thicken at one end and thin 

 out at the other, with an appearance almost like that of pulsation, 

 repeating this process many times. Again, a single mitochondrium 

 sometimes twists and turns rapidly, as though attached at one end, like 

 the lashing of a flagellum, then suddenly moves off to another position 

 in the cytoplasm as though some tension had been released. Corre- 

 sponding to the forms observed in the stained preparations, we find in 

 the hving cells that granules can be seen to fuse together into rods or 

 chains, and these to elongate into threads, which in turn anastomose 

 with each other and which may unite into a complicated network, and 

 in turn may again break down into threads, rods, loops, and rings. 



The work of M. R. and W. H. Lewis includes also most interesting 

 experimental researches on the influence of chemical agents, heat, and 

 hypotonic and hypertonic solutions on the mitochondria, which open a 

 large field to further investigation. Regarding the connection of the 

 mitochondria with other granules, as well as with cytoplasmic differ- 

 entiation, these authors are rather skeptical. They believe that the 

 mitochondria are in all probability bodies connected with the metabohc 

 activity of the cell. 



Studying the fertilization of Ciona intestinalis, J. Duesberg reaches 

 the conclusion that the whole spermatozoon, head, tail, and mito- 

 chondrial body, enters the egg, but he is unable to determine the fate 

 of the mitochondrial body in the egg. 



The egg itself shows at its vegetative pole an accumulation of mito- 

 chondria. At the expense of this part of the egg are formed the muscle- 

 cells, which throughout the cleavage are characterized by their con- 

 siderable amount of mitochondria. The other cells of the embryo show 

 also constant cytological differences. The entoderm and the chorda 

 cells are filled with yolk granules and contain only very few mito- 

 chondria; in the ectoderm cells, mitochondria and yolk are about equal 

 in quantity, while the neural plate cells contain a few more mito- 

 chondria than do the ectoderm cells. Finally, the appearance of the 

 mesenchyme cells is very striking, owing to the fact that they contain 

 very few granules of any kind. 



The conclusion is that the differences shown by the various kinds of 

 cells of the embryo are not due to the presence of different organ- 

 forming substances, but to a regular and peculiar distribution between 

 them of the formed elements contained in the egg. 



The work of Professor H. M. Evans on the macrophages is closely 

 connected with his previous studies on the behavior of the different cells 

 of the organism towards the vital dyes (see former report) . His conclu- 

 sions are that the macrophages may be defined as those mono-nuclear 

 cells, w^herever they may be, Uning vascular channels, resident in the 

 connective tissues or entirely free, whose protoplasm constitutes a 



