MORPHOLOGY OP BRAIN AND SENSE ORGANS OF LIMULUS. 39 



B. There is some doubt in regard to the position of the 

 Gustatory Centre. I did not have this point so much in 

 mind during these experiments following section of the crura, 

 and I did not always test for gustatory reactions. The centre 

 for the mandibular gustatory organs probably lies in the fore- 

 brain. One would naturally suppose, however, from the way a 

 given leg can be made to chew when its gustatory organs are 

 stimulated, that there was in each leg an independent gustatory 

 centre, which I at first supposed might be located in the 

 ganglion of the pedal nerves. However, if this be so, it is 

 hard to understand why sectioning either the ventral cord, or 

 the crura back of the fore-brain, should stop the reflexes, while 

 a median longitudinal section across their union in the vagus 

 region should have no eflPect (see pp. 37-8). There is also a 

 difficulty in the fact that I have amputated the whole leg, 

 including a portion of the crura with the attached pedal nerve 

 and its ganglion, and on stimulating the gustatory spines with 

 food have failed to produce reflex contraction of the leg, 

 although movements could be easily produced by applying 

 the electrodes directly to the pedal ganglion or nerve. 



c. Structure of Temperature Organs. — It is not so 

 easy to identify the temperature organs as the gustatory ones. 

 However, I have found close beneath the epidermis, in all the 

 parts examined, including various regions on the upper and 

 lower walls of the carapace, the gills, the legs, &c., a loose 

 subdermal plexus of nerve-fibres and ganglion-cells. The 

 cuticula of all these regions is perforated with canals under 

 which are buds, in nerve-supply and structure like those in 

 the mandibles and in the olfactory region. As I can find 

 nothing else there that looks like sense organs, it is very 

 probable that these buds are the organs that are specially 

 susceptible to changes of temperature. 



D. Function, — The temperature sense seems to be remark- 

 ably acute in Limulus. I know of no other Invertebrate that 

 approaches it in this respect. As Limulus spends the fall and 



