72 THE BIOLOGY OF HYDRA : 1961 



cells. In cases where the intercellular bridge is long and slender and 

 still contains the relic of the mitotic spindle apparatus (Hirschler's 

 fusome) the structure may bear a strong resemblance to a nerve 

 fiber, especially in silver preparations where the fibers take the 

 stain like nerve fibers. I suspect that such fibers may have been 

 mistaken for nerves by certain workers. 



"Innervation" of cnidohlasts. Given the abundance of neurites 

 and cnidoblasts it is not surprising to find frequent instances where 

 the two are in contact (Fig. 5). A rough estimate suggests that 

 about one in five cnidoblasts are in contact with part of a neuron or 

 neurosensory cell. No cases have been found where a neurite termi- 

 nates directly upon a cnidoblast such as Spangenberg and Ham 

 describe in H. litforalis. The contacts are apparently quite casual and 

 undifferentiated. Perhaps we should not speak of innervation until 

 we can show that these associations have functional significance. 

 Comparison of Cordijlophora and Hydra. Hydra has proved 

 harder to examine than Cordijlophora because the tissue is histologi- 

 cally denser and more elaborate. However, the silver preparations 

 do quite clearly show nerve elements. All that can be said at this 

 stage in the work is that the system appears generally similar to 

 that of Cordijlophora. Conventional neuro-sensory cells (Fig. 10) 

 such as Hadzi describes have been seen as well as subepithelial 

 ganglion cells (Fig. 12), some of which have a rudimentary hair 

 such as occurs in Cordijlophora. If there is a noteworthy difference 

 between the two forms it would seem to be the greater tendency 

 in hydra for neurites to run in bundles. This has been seen near 

 the hypostome, where bundles of up to four or five neurites (Fig. 

 11) have been followed for short distances, running around the ani- 

 mal in a circular direction. As to the connections, which many claim 

 to be continuous, I have nothing to say at the moment, except that 

 I have not seen any junctions which I would confidently interpret 

 as being continuous. 



HESS: Does anyone else have any comments? 



CLAY BROOK: 1 am very sorry that Dr. Spangenberg of the 

 Texas group was not able to attend this meeting to present her 

 studies of the nervous system in H. littoralis. I am afraid 1 cannot 

 do a very good job of describing her methods and conclusions. 



