152 



OHAS. B. WILSON. 



2. If spin-threads are outflows of internal proto- 

 plasm, their activities must be similar to those in 

 the interior of the egg — a conclusion reached from other 

 material by G. F. Andrews (4). 



One of the activities of the spin- threads is a streaming 

 movement of their more liquid contents. Unfortunately the 

 blastomeres are so opaque that we cannot see whether there 

 is a corresponding internal flowing of the protoplasm, but it 

 hardly seems possible that the former could exist without 

 the latter. Such streamings of the egg protoplasm have 

 been witnessed by Erlanger (21) in the living eggs of several 

 small Nematodes which are transparent enough to show it 

 distinctly. 



In each end of these eggs alternately the protoplasm moved 

 from the poles to the equator, but as soon as the equatorial 

 groove appeared the streaming turned inward at the groove 

 and then backward toward the pole. After the first seg- 

 mentation similar streamings appeared in the blastomeres. 

 These movements were vigorous enough to distort the cleavage 

 spindle, and Erlanger concluded that the whole of the egg, 

 spindle and astral rays included, is always plastic and fluid, 

 though the rays are more viscid than the remainder. Blunt 

 pseudopodia were formed on these nematode eggs at various 

 points, especially near the edge of the cleavage groove, but 

 no spin-threads were noticed. 



The observation of such phenomena in transparent eggs 

 furnishes a strong presumption in favour of their occurrence 

 in opaque eggs, particularly in connection with such vigorous 

 external movements. 



3. The spin-threads and other cytoplasmic con- 

 nections assist materially in appression, and proba- 

 bly in other movements of the blastomeres. 



The spin-threads possess a contractility of sufiicient 

 strength to move the blastomeres, and there can be no doubt 

 that they assist in drawing them together after segmentation. 



They produce visible motion after the first cleavage, but 

 not in any succeeding stage, because the physical conditions 



