Smallwood and Rogers, Molluscan Nerve Cells. 47 



are similar to those that occur in this structure in ova in most 

 animals during their growth. The vacuoles that occur in the 

 nucleus are not as common and it is doubtful whether they are 

 normally present. So far as we are aware they have not been seen 

 in the living nerve cells, but are common in cadaveric specimens. 

 Nerve tissue poorly fixed may also exhibit them, which renders it 

 all the more probable that they are artefacts. 



The vacuoles in the cytoplasm are present in the nerve cells of 

 many animals both vertebrate and invertebrate. They can be 

 seen in the living nerve cells of Gasteropods and have been reported 

 in some vertebrate nerve cells. In well fixed and stained sections, 

 vacuoles are very commonly found which agree in form and appear- 

 ance with the conditions in the living cells. Considerable work 

 has been done to determine the, question whether or not these 

 cytoplasmic vacuoles have a definite wall. It is necessary in this 

 connection to distinguish the vacuoles from the lymph spaces and 

 capillaries. The vacuoles are usually small and irregularly dis- 

 tributed throughout the cytoplasm. They contain a homogenous 

 fluid or differential bodies, and their presence is, we believe, inti- 

 mately associated w^th the metabolism of the cell and probably 

 with its constructive phases. These vacuoles vary in number in 

 the same animal and in the same species. This would indicate 

 that they are transitory structures which appear when certain 

 chemical changes occur, and then disappear. A very critical 

 study of the cytoplasm in contact with the vacuoles fails to show 

 any evidence of a separate wall. The vacuole in the living nerve 

 cell forcibly reminds one of the food vacuoles in protozoa which 

 appear to have a wall; but this appearance is really due to the con- 

 tact of fluids of diff^erent refractive index. In stained specimens 

 the vacuoles look as if they were limited by a more deeply staining 

 border, but this may be explained as due to the accumulation of 

 cytoplasmic granules about the enclosed liquid. We believe that 

 it is no more proper to speak of a wall for these vacuoles than it is 

 to say that the numerous vacuoles in a protozoan have walls. 



The lymph spaces are of a different character and are usually 

 located in the periphery of the cytoplasm. They are intimately 

 associated with the circulatory system and may contain blood. 

 In some of the larger invertebrate nerve cells the periphery is 

 richly supplied with lymph canals which may occasionally con- 

 tain corpuscles. These canals or spaces can in many instances 



