NOTES AND MEMORANDA. 559 



fibres can themselves aid in the multiplication of nerve- 

 fibres. 



According to Ranvier the constrictions are the points of 

 greatest nutritive activity in the medullated fibres. It is 

 probable, therefore, in the case of embryonic nerves, that 

 these are also the points where the greatest amount of forma- 

 tive energy is manifested. 



The deposit of nerve-medulla does not always proceed with 

 the same regularity in all fibres. As a rule, the length of 

 the segments decreases gradually from their origin to their 

 peripheral termination. Sometimes the medulla is developed 

 on alternate segments, leaving out the intermediate portions. 



Summing up his views on the formation of the medullary 

 sheath, Leboucq concludes this portion of his memoir in 

 the following statements : 



The parietal nuclei are derivatives of the embryonic cells, 

 and are found in the substance of protoplasmic masses or 

 plates surrounding the bundles of fibrils. These nucleated 

 masses correspond to the '' Hautchenzellen" of Axel Kev 

 and Retzius. 



Each nucleus corresponds to a special area of the sheath 

 of one bundle of fibres. 



Each protoplasmic cell-mass {" Hautchenzelle") corre- 

 sponds to one segment of medulla, the limit between two 

 neighbouring cells constituting a constriction. 



The nerve-medulla is developed by a chemical metamor- 

 phosis of the elements surrounding a bundle of fibrils, not, 

 as KoUker holds, by a transformation of the peripheral fibrils 

 of a bundle. 



The Peripheral Nerve Terminations. — This division of the 

 paper commences with a preliminary account of the struc- 

 ture of the epithelial covering of the skin of the animals 

 examined. Attention is drawn to a peculiar form of cement- 

 substance between these epithelial cells. This cement-sub- 

 stance has a peculiar dotted appearance, like a " row of 

 pearls." 



Leboucq next proceeds to describe two kinds of cells found 

 in the deeper layer of the epithelial covering of the skin, 

 corresponding to the human rete Malpighii. These cells 

 are believed to be in connection with the nerve endings. 

 The first sort are finely granular, branched corpuscles, about 

 3 to 6 mm. in breadth and 25 to 30 mm. in length. These 

 corpuscles, which are placed between the epithelial cells, 

 are coloured by osmic acid, like nerves, but show neither 

 nucleus nor nucleolus. 



The processes of these corpuscles can almost always be seen 

 to be in connection with nerve fibrils, sometimes with fairly 



