Observations also were made by phase microscopy to check the rate of dissociation of the neurons and any potential degenerative changes with enzyme incubation, such as perikaryal swelling or segmentation and loss of processes.
There are four morphological types: (1) a 3-7-[[micro]meter]long cilium with a 1-2-[[micro]meter]-long neck, an 8-11-[[micro]meter]-long tapered perikaryal region, and a long unbranched axon with a simple terminal [ILLUSTRATION FOR FIGURE 5 OMITTED]; (2) a 7-8.3-[[micro]meter]-long cilium rising from the enlarged apex of a narrow 7-16-[[micro]meter]-long neck [ILLUSTRATION FOR FIGURE 6 OMITTED]; (3) a 4-7-[[micro]meter]-long cilium extending from a 1.5-7.7-[[micro]meter]-long neck and a short oppositely directed axon, which bifurcates into two long terminal processes [ILLUSTRATION FOR FIGURE 7 OMITTED]; and (4) a short, curved, neck-like process with a 5-6-[[micro]meter]-long apical cilium and a slender axon with a pair of terminal swellings having twig-like processes (not shown by SEM).
Morphological types include (1) a short, 2-4-[[micro]meter]-long, perikaryal cilium with two lamellar processes [ILLUSTRATION FOR FIGURE 15 OMITTED]; (2) tiny cells with short, straight isopolar processes [ILLUSTRATION FOR FIGURE 16 OMITTED]; (3) asymmetrical cells with one short knobbed [ILLUSTRATION FOR FIGURE 17 OMITTED] or tapered [ILLUSTRATION FOR FIGURE 18 OMITTED] and one long process; (4) cells with one simple and one complexly branched process [ILLUSTRATION FOR FIGURE 19 OMITTED]; (5) cells with an elongated perikaryon that is 10-12 [[micro]meter] long and 5-7 [[micro]meter] wide with thick bifurcated processes [ILLUSTRATION FOR FIGURE 20 OMITTED].
A few multipolar ganglion cells, all tripolar, have a perikaryal cilium (not shown by SEM).
Although some damage to processes and perikaryal shape changes may have occurred in the preparations, they did not alter our ability to categorize the major cell types.
Neurons dissociated from Hydra littoralis and divided into those with an apical cilium (sensory cells) and those with no cilium or a perikaryal cilium (ganglion cells) were further categorized into unipolar, bipolar and multipolar types based on the number of identifiable processes extending from the perikaryon (Yu et al., 1986).