1906.] 



Cell Communications between Blastomeres. 



503 



cell to cell by means of such delicate threads. It is highly probable that 

 the strands described here between blastomeres can play an important part 

 in a similar manner. 



In nearly all plant tissues, the cell walls are traversed by delicate strands 

 or intercellular bridges of protoplasm. The work of Gardiner (3), Kienitz- 

 Gerloff (5) and Meyer (7), has conclusively proved among plants how wide-spread 

 and universal is their distribution. It is almost possible to speak therefore of 

 plants as multinucleated masses of protoplasm or Syncytia. Meyer (7), as the 

 result of his studies on Volvox, comes to the conclusion that " Plasmaverbin- 

 dungen zwischen alien Zellen eines jeden Individuum dadurch vorkommen, 

 dass das thierische und pfliinzliche Individuum charakterisirt ist, dass es 

 eine einheitliche Cytoplasmamasse besitzt, dabei eine einkernige Zelle, eine 

 vielkernige Zelle oder ein System von Zellen sein kann, deren Cytoplasma 

 ein zusammenhangendes Ganzes bildet," p. 212. 



Among animals, undoubted cases of true syncytia occur not infrequently in 

 the centrolecithal eggs of Arthropods. Here the nucleus takes up a central 

 position, dividing into two, four, eight, and sixteen or more cells, while the 

 egg as a whole has remained unsegmented. The nuclei make their way to 

 the surface of the egg there taking up their respective positions ; at a later 

 stage only after this has taken place, does the cytoplasm split up into as 

 many cells as there are nuclei. 



In Peripatus, according to Sedgwick (11) the cleavage takes place as in 

 centrolecithal eggs, but the segmentation nucleus divides at the periphery 

 instead of the centre of the egg. The first division separates the opaque area 

 into two portions that lie closely applied to one another. A careful 

 examination, however, shows " that the furrow has- not completely separated 

 the two segments from each other, but that they are connected by strands of 

 protoplasm forming a loose network between them, the embryo at the 

 gastrula stage, and in all the earlier stages of development, is a syncytium," 

 p. 24. Sedgwick holds that even in later stages, and also in Vertebrates, the 

 entire body is one continuous syncytium. " The primitive streak, the walls 

 of the ccelom, and the neural crest, and parts of the ectoderm, are growing 

 points where nuclei, not cells are produced." He cites in particular 

 the case of the third nerve in Selachians, which he claims along with other 

 nerves is differentiated as a portion of a continuous reticulum. Amongst 

 adult epithelial and connective tissue cells connections or bridges were earl}' 

 described by the old school of histologists as Max Schultze (1864 , 

 Bizzozero (1872), Eanvier, Hemming (1876), Heitzmann (1883) and recently 

 Schuberg (9) has added a long contribution to the subject in which many of 

 these early results are confirmed. 



vol. lxxvii. — b. 2 o 



