500 



Mr. C. Shearer. On the Existence of [Jan. 30, 



present at a slightly later stage. In living material, strands such as these are 

 seen to arise as the gradual separation of the cells takes place to form 

 the segmentation cavity ; so in some cases they would seem not to be new- 

 formations, but the stretching of former connections. For instance, the 

 strand in fig. 1, can be sometimes seen to form as the cells are separated by 

 growth, by the drawing out of their former point of contact, their ends being 

 in touch with one another at an earlier date. 



Fig. 4, is also taken from a section of a Eupomatus egg, but this time fixed 

 with Hermann's fluid. In this case a distinct ridge is cut across, but no cell 

 boundary can be distinguished. The protoplasm granules are continuous 

 without interruption from one cell to the other. 



Fig. 5, is a section of a partially-formed gastrula of Eupomatus. Here one 

 of the endoderm cells has joined two of the ectoderm cells. But at the point 

 of contact no cell wall can be distinguished. The upper of the two ectoderm 

 cells making the connection, probably belongs to the " apical rosette cells," and 

 the entomere with which it forms the connection is possibly the cell shown 

 in fig. 3 (marked en) at a later stage. This connection may have remained 

 unbroken from the first. 



Fig. 6, is a gastrula of Eupomatus fixed with corrosive and acetic. The 

 ectoderm and endoderm are joined by strands which are continuous with 

 cells in each layer. These strands may represent mesenchyme cells, but 

 at this stage they would seem to be joined alike to cells in both germ layers. 



Fig. 7, is a section similar to some of the first. The strands in this case are 

 decidedly filose in character. 



Fig. 8, is a section of a gastrula of Polygordius fixed with Corrosive- 

 acetic. A large entomere is seen continuous with a conspicuous cell of the 

 ectoderm. 



Numerous other examples could be given, but it is unnecessary to add to 

 their number, as in all cases the strands are of quite the same nature. There 

 can hardly be any doubt that they are similar if not identical with the filose 

 filaments described by Andrews (1), as already mentioned, and which he 

 expressly states sometimes " varied from fine filaments to broad bridges." 

 He has observed them on the living eggs of a number of Echinoderms, 

 Annelids, Molluscs, and Nemertines, and traces of their presence in preserved 

 eggs of Amphioxus and Amphibia. He says, " the most delicate filose 

 displays were seen near the polar bodies during the first and second cleavages. 

 The egg put forth fine protoplasmic threads that branched and reached up 

 towards the second polar body, and the filose phenomena in it led to the 

 assumption that it was a flowing mass of protoplasm " (p. 5). According to 

 Andrews, who believes they "furnish a medium for co-ordinating the 



