BRANCHIAL WARTS. 115 



The thick epidermis is heavily pigmented, and pigment is frequently seen 

 in the body of the sensory cells. 



The sense buds are so numerous that their inner ends are crowded together 

 several rows deep. The inner surface of the sensory field is very vascular, and 

 the narrow crevices between the organs are often crowded with blood corpuscles. 



The posterior wall of the flabellum, in marked contrast to the anterior, con- 

 tains few or no sensory perforations, and the epidermis is thin, nearly colorless, 

 and with few blood-vessels. 



The flabellum is supplied by a very large nerve the root of which passes over 

 the neural surface of the sixth pedal ganglion and joins the main gustatory tracts. 

 It does not differ from the fascicles coming from the gustatory cells in the man- 

 dibles, except that it is larger. It appears to form the greater part of the conspic- 

 uous neuropile enlargements seen on the median face of each crus. (Fig. 65.) 



The flabellum doubtless serves to test the quality of the water that is drawn 

 into the gill chamber. I have not been able to detect any characteristic reactions 

 when it is stimulated. 



The flabellum probably represents the exopodite of the sixth pair of append- 

 ages. Traces of similar organs are seen for a short time at the base of the other 

 appendages. (Fig. 141.) 



The Branchial Warts. The branchial warts are blister-like elevations about 

 four mm. in diameter, located on the endopodites of the branchial appendages. 

 They are covered by a soft, bluish chiten, and lie either folded over the margin, 

 half on each side of the gill, or in pairs, one member on the anterior, the other 

 opposite to it on the posterior surface of the appendage. (Fig. 82.) 



The outer surface is thickly and uniformly covered with goblet, or bell- 

 shaped hairs, deeply set in conical recesses. There are two distinct sizes, evenly 

 distributed in about the proportion of five small ones to one large. The large 

 bell-shaped hairs lie over the outer ends of large canals which contain spirally 

 coiled, and very distinct chitenous tubules. (Fig. 85, Br. and C.) 



The canals are colorless and, except for the tubule, appear to be empty. 

 They do not contain blackened fibers or nuclei such as occur in the flabellar 

 canals. The tubule springs from a small, fusiform cluster of sensory cells lying 

 well below the surface. Thick nerve bundles, remarkable for the large ganglion 

 cells scattered over them, leave the inner ends of the cell clusters and uniting with 

 the other bundles form a loose nerve plexus, which is continuous with termina 

 branches of the branchial nerve. 



The smaller goblet hairs are without visible tubules, and their faint, under- 

 lying canals do not perforate the outer chitenous layers. They do not appear 

 to be connected with nerves. 



The inner surface of the flexible chiten that covers the branchial warts ex- 

 tends inward in the form of thin, vertical walls that form a coarse, polygonal 



