1885.] NATURAL SCIENCES OF PHILADELPHIA. 377 



On the Pectoral Filaments in the Sea Robin (Primotus palmipes). 

 — Dr. Harrison Allen said, in speaking of the pectoral flu of 

 the family of teliostean fishes, the Triglidce, that the first three 

 rays are known as the pectoral filaments. They are disposed 

 ventrally, separated from the bod}' of the fin, and placed well in 

 front of its base. The filaments are curved somewhat upon them- 

 selves, and are moved by powerful muscles. The nerves supply- 

 ing them are derived from the ganglionic masses (so character- 

 istic of the Triglidae) at the beginning of the spinal cord. The 

 filaments are used not only for touch but for locomotion. In 

 directing the body toward the right, the left filaments are in 

 constant motion (like the limbs of a salamander) while the right 

 filaments are at rest. In directing the body toward the left, the 

 motion thus described is reversed. The filaments are also used 

 in stirring up the soft silt which composes the bottoms on which 

 the fish rests. The organs are thus put to comparative rough 

 usage, so that one learns with a sense of surprise that the tops 

 and sides near the tips possess a high degree of differentiation of 

 the tegument. The organ, while appearing to be tactile in nature, 

 recalls in character the general features of a retinal surface. Both 

 in longitudinal and in transverse section the organ is seen to be 

 composed of four layers of cells. The first basal laj-er is made up 

 of small nearly round cells. The second la} - er is composed of large 

 fusiform cells, each of which contains granular contents surround- 

 ing a distinct circular nucleus. The third layer is composed of 

 columnar cells resembling finger-like processes which arc arranged 

 like a layer of retinal rods. A connective tissue membrane which 

 might be compared to the external limiting membrane of the retina 

 intervenes between the third and second layer of cells. The 

 fourth and peripheral layer is composed of diaphanous tube-like 

 prolongations of the side of the cells which compose the third 

 layer. It varies greatly in thickness. In some portions of each 

 filament the fourth layer is very thin, and barely covers the tips of 

 the processes of the third layer, or it is of a thickness nearly 

 equal to one-half the thickness of the entire organ. The layer 

 appears to be tightly held to the third, and is often detached in 

 the sections. The general membrane is smooth and uniform at 

 the tips of the filaments, but is arranged in broad capitate 

 papillae elsewhere. 



The recorder thought the pectoral filaments to be beautiful 

 objects for study. They can be readily obtained since the sea- 

 robin is a common summer fish along the Atlantic coast. 



September 22. 

 The President, Dr. Leidy, in the chair. 

 Twenty-five persons present. 



