IN A PAPER on "Progressive Hypertrophic Interstitial Neuropathy of Infancy," Dejerine and Sottas1described the clinical and pathologic features of a recessively inherited, severe, mixed peripheral neuropathy with enlargement of nerves. Subsequently, the enlargement of nerves seenclinically and postmortem and the histologic features of onion-bulb formations were found to be associated with disorders which seemed to be different, as judged by their natural history, pattern of inheritance, and biochemical alterations.2-8 In reports based on light-microscopic examination of peripheral nerves, there has been some disagreement on the origin and cellular composition of the onion-bulb formation (also called "cuff" or "whorl"). The majority of authors favored a Schwann-cell origin,6,9-19though a few of them noted a connective-tissue constituent in the whorl.14,15Dejerine and Sottas,1and particularly Dejerine20with AndréThomas,2and others22-26favored a connective-tissue origin. That myelinated fibers lay at the center of