[chambers] microdissection OF CELLS 45 



The surface layer of the egg cell is dense in consistency when 

 compared with the cell interior into which it merges insensibly. In 

 the unfertilized egg, the cell granules are imbedded in it up to the very 

 line of division between the egg and surrounding medium. With the 

 needle the surface may be pulled out into long strands without other- 

 wise disturbing the contour of the ceU. On being released the strands 

 tend to curl and retract slowly till they disappear. If a more rapid 

 tear be made, and if the cell be under compression, the spot torn 

 bulges out as the internal cytoplasm presses on the weakened surface. 

 The surface layer of the swelling protuberance is very easily broken, 

 upon which the interior may pour out. The cytoplasm then either 

 disintegrates entirely in the surrounding water or,.if remaining normal, 

 reestablishes a film on its surface. When left undisturbed the new sur- 

 face film gradually strengthens into a definite ectoplasmic layer and the 

 protuberance slowly retracts until the original contour of the egg is 

 reestablished. If the point of attachment of the protuberance be 

 small, the protuberance may be pinched off to form a spherule of 

 cytoplasm which to all appearances is normal. 



In summary, we may say that the surface layer is a highly exten- 

 sile, contractile and viscous gel capable of constant repair. Its 

 establishment and maintenance is a property essential to protoplasm. 

 With the film intact the mass of protoplasm maintains itself and the 

 life of the cell is assured. When the film is destroyed the cytoplasm 

 flows out, the cell granules swell and disappear, the whole mass com- 

 pletely disorganizes and disappears in solution in the surrounding water. 



The egg cell of Solaster. The Solaster egg is very large when 

 compared with other Echinoderm eggs, being well over 1 mm. in dia- 

 meter. This is partly due to the fact that it is heavily laden with 

 yolk. The nucleus, however, is also very large, so large in fact that 

 it is visible to the naked eye and can be easily isolated with needles 

 under an ordinary dissecting microscope. Its enveloping surface 

 film exhibits a distinct resistance to compression. Tearing the surface 

 allows the fluid contents to escape and the nuclear wall collapses. 

 The Solaster egg appears to be the only case on record of a Metazoon 

 cell of which the nucleus is large enough to be actually handled and 

 dissected with ordinary needles. 



Conclusion 



In conclusion, one may make the following statements with 

 regard to the consistency of the living cells which were dissected : 



1. The cytoplasm of an &gg cell consists of a semi-liquid interior 

 enclosed in a jelly-like and highly viscous surface layer. The surface 



