Studies on the Structure of the Golgi Apparatus. IV. Endostyle of Branchiostoma indicum.

Abstract

The work on Branchiostoma was undertaken with a view (1) to study the relation between the central and Golgi apparatus in a ciliated cell where the parts of the central apparatus are supposed to be associated with the cilia, and (2) also to see whether any hint as to the mode of evolution of the network can be obtained. Each group of mucous secreting cells seems to be in a particular stage of activity. The variations in activity between the individual cells in a particular group is very small. It was observed that generally, while two groups of gland-cells are loaded with mucus, the other two are at the beginning of the secretory cycle. The mitochondria, which appear as a few large grains in the cells at the beginning of secretory activity, break up into small granules before mucous droplets put in their appearance. Most of these mitochondrial granules are extruded with the mucus. The Golgi apparatus occurs as a few small grains having an indefinite distribution. There is no ‘Golgi zone’, nor are these elements collected around a centriole. These increase in size and number and as they do so in many of them the central area becomes brownish. The Golgi elements finally get scattered through the cell. This scattering is soon followed by the appearance of mucus in the chromophobic areas of the elements. Increase in size of secretion droplets leads to rupture of the osmiophilic portion in regions where it is thin, and mucous globules with Golgi caps may be seen in the cytoplasm. Most of the Golgi elements degenerate, and those left behind apparently become reorganized for the next secretory cycle. Examples and results are cited to show that the chromophobic part has nothing to do with the centrosphere. It appears difficult to decide whether the presence of Golgi apparatus in the form of discrete elements is the retention of an invertebrate characteristic by Branchiostoma. The recent conclusions of Hirsch and Duthie are discussed, and it is shown that unless equal importance is given in future studies to the shape and structure of the Golgi apparatus and mitochondria as is at present given to the function of these cytoplasmic components we cannot accept the claims put forward by these authors. There appear to be exceptions to every rule, and in order to accept these as exceptions critical evidence is necessary.