88 



NERVOUS SYSTEM OF VERTEBRATES. 



42, 43), dendrites are fused with dendrites into an intricate net- 

 work. In other cases neurites are fused with the protoplasm 

 of other nerve cells instead of merely ending in contact with 

 them. That part of the neurone theory which states that nerve 

 cells make connections with one another only by contact is defi- 



FiG. 44. — Two ganglion cells of the nervous network in the intestinal wall of the 

 leech, Pontobdella, showing neurofibrillae passing through the cells. From Bethe 

 after Apathy. 



nitely disproved. Other criticisms which have been brought 

 against the neurone theory are rather in the nature of extensions 

 and corrections of the conception of neurones. 



The relationships of the neurofibrillae have been represented 

 as antagonistic to the neurone theory. Although the existence 



