Il6 GENERAL AND SPECIAL CUTANEOUS SENSE ORGANS. 



network when seen in surface views. They are covered with a thick epithelium* 

 giving them in sections a false appearance of sensory infoldings. 



Between two opposing organs is a loose, areolar tissue and a conspicuous 

 venous chamber. 



These organs are clearly of a very special kind. In addition to their unusual 

 naked eye appearance, they are peculiar in the shape of the terminal goblet hairs; 

 in the absence of cells or fibers in the underlying canals; in the thick walled, spiral, 

 chitenous tubule; in the ganglionated nerve branches, and in their inflated elastic 

 walls that lie on opposite sides of the appendage. 



Their peculiar structure indicates that they may be provisionally regarded 

 as a kind of pressure guage which aids in the control of the heart beat and the 

 respiratory movements. 



The Slime Buds. Slime buds are spherical masses of glandular cells, mingled 

 with nervous or sensory ones, and richly supplied with nerves. 



They vary greatly in their grade of development, and in the relative number 

 and size of their sensory and glandular cells. They are scattered over the whole 

 surface of the body, but are especially abundant in certain regions, or areas, that 

 are known to be highly sensitive. 



While at first sight they appear to be merely integumentary glands, closer 

 examination raises many important questions that are difficult to answer, as, for 

 example, in regard to their function, minute structure, and development. 



It is probable that they play an important part in the reactions toward certain 

 kinds of stimuli, but whether their secretions serve to protect the adjacent 

 nerve buds against excessive stimulation (which seems to me very improbable), or 

 as absorbers and intensifiers of certain substances, has not been demonstrated. 



A familiar illustration of a similar condition in vertebrates is the association 

 of slime, or mucous cells with the sense organs of the lateral line. There is also 

 an intimate association of mucous and sensory cells in many molluscs, i.e., in 

 Lima, Area Noas, and in the tentacles of Haliotis. 



The facts that have special significance for our problems are as follows: 



1. Secretion of mucus. When small Limuli are violently stimulated, the 

 slime buds discharge an abundance of mucus, and, if the surface of the shell 

 has been previously wiped dry, it may be seen to collect in small drops over each 

 pore. When allowed to accumulate, it forms a thick slimy covering to the whole 

 surface. 



2. Distribution. The slime buds are very numerous in certain well defined 

 areas which, from their location and abundant nerve supply, have every indication 

 of being highly sensory, as, for example, in the olfactory organs, in the mandibular 

 spurs of Limulus, and the maxillaria of the second and third pairs of thoracic 

 appendages in the scorpion. 



3. Innervation. These groups of slime buds are innervated by special nerves, 



