40 WILLIAM PATTEN. 



winter months in deep water, where there is comparatively 

 little variation in temperature, it is hard to imagine what this 

 sense can be used for if not to aid the animal in mi- 

 grating to warmer shallowwater during the breeding 

 season. 



V. Tactile Sense. 



There are some wart-like sense organs about 5 mm. in 

 diameter on the endopodites of the abdominal appendages, to 

 the structure and function of which I have not given special 

 attention. They have already been briefly described by 

 Gegenbaur. The underlying cuticula is richly perforated 

 with peculiarly shaped canals, and chitinous tubules extend 

 into them similar to those in the gustatory spines. They are 

 sensitive to ammonia vapour, tactile impressions, and tempera- 

 ture changes, but stimulation of them in this way does not 

 produce any definite reflex action. If a camePs-hair brush be 

 drawn gently across the terminal joint of the expedites to the 

 abdominal appendages, or over the region about the olfactory 

 organs on the abdominal appendages, prompt movements of 

 the legs and abdomen follow. This is not the case when the 

 basal joints of the legs, or the soft flexible skin about the 

 joints of the legs, or about the anus, are brushed. 



VI. Summary. 



If we review the results of our observations described in the 

 preceding pages, we see that there are two distinct kinds of 

 sense organs in Limulus. There are the single-celled sense 

 organs, each with a long chitinous tubule, the best representa- 

 tions of which are found in the mandibular spines and in the 

 chelae of all the walking appendages; they are pre-eminently 

 gustatory: a slightly modified kind in the chelae probably serve 

 as temperature organs. 



The second kind are rounded, solid clusters of gland-like 

 cells, containing a large multipolar ganglion-cell provided with 

 a chitinous tubular prolongation, the distal end of which 



