Smallwood and Rogers, Molluscan Nerve Cells. 55 



Bethe ('00). We have here to do only with dependent canals (blood vessels) 

 which can be proven only by injections. No nuclei are to be found in the walls of 

 these canals. The canals result from the fusion of separate vacuoles. The canals 

 have nothing in common with the neuro-fibrillae (Fig. 4). 



IV. VACUOLES. 



The presence of vacuoles or vacuolar-like structures in the cyto- 

 plasm of nerve cells is a common structural character. They 

 have been recorded as follows: 



Hodge's ('92, '94) work is of great importance to all interested in the question 

 of fatigue and the accompanying structural changes in the nerve cells. The spinal 

 ganglion cells of the frog, cat and dog, under electrical stimulation and the spinal 

 ganglion and brain cells of English sparrow, pigeon and swallow show the follow- 

 ing changes. The nucleus undergoes a marked decrease in size and changes from 

 a smooth and rounded structure to one having a ragged outline. Its reticulate 

 appearance is changed and the whole structure takes a denser stain. The cell 

 protoplasm gives evidence of slight shrinkage and the formation of vacuoles. These 

 vacuoles appear quite constantly in the ganglion cells of birds. The vacuoles have 

 a sharp outline and a definite shape in the rested animal but are indistinct in the 

 bird that has been at work during the day. Vacuoles also appear in the honey bee 

 under the following conditions. Honey bees were collected in a raspberry patch 

 as soon as they appeared in the morning. The first six bees were quickly decapi- 

 tated, the brains removed, and three were dropped into one-half per cent osmic 

 acid, and three into saturated mercuric chloride solution. At about seven o'clock 

 at night six more bees were captured and treated in the same manner. After 

 the morning and evening bees had been paired at random, each pair was stained 

 and studied and an attempt was made to measure the nuclei and work out the 

 amount of shrinkage. The minimal shrinkage was 9 per cent, and the maximal 

 75 per cent. The author does not attach much value to these figures, although 

 they express the fact that a wide difference exists between the two. The average 

 in diameter of the morning bees is more uniform than for the evening bees. These 

 results indicate first, that the nerve cells of a number of bees' brains are in a more 

 uniform condition in the morning than in the evening. Secondly, they differ in 

 appearance, or condition, from one another, somewhat in the morning and a great 

 deal in the evening. 



Montgomery ('97) finds in the nemerteans, Cerebratulus and Lineus, chromo- 

 philic corpuscles under the following conditions: The cytoplasm of the medium 

 sized cells is of a coarsely vacuolar structure; sometimes the hyaloplasm fills the 

 whole proximal portion of the cell as far as the nucleus. But a thin, peripheral 

 layer of spongioplasm is always present, and a similar layer envelops the nucleus. 

 These cells are much larger in Cerebratulus and the cytoplasm is much denser, 

 t. e., there is a proportionately greater amount of spongioplasm, and a coarsely 

 vacuolar structure is seldom found. The large cells of the brain are of an elongated 

 pyriform shape, largest and rounded proximally, seldom nearly spherical. It may 

 be noted that while the cell bodies vary considerably in size, their nuclei remain 

 of nearly uniform dimensions. The cytoplasm is, as a rule, coarsely vacuolar 



