130 The Mouth in Ricimdei and in Insects. Organs of Sense 



most, handbooks we find the first pair of limbs in Arachnida mentioned as mandibles, in entire 

 disregard of the view propounded by Latreille, Claparede, and Huxley, and by them founded 

 on comparative considerations of anatomy and embryology, viz. that the first pair of limbs 

 in Arachnida is the homologue of the antennas (rather of one of the two pairs of antennae) 

 in other Condylopoda. Authors who held the view that those limbs are mandibles would 

 scarcely have failed to lay stress on the apparent similarity in the structure of the mouth 

 in Ricinulei and in Insects, as a decisive argument in favour of looking upon Arachnida as 

 being nearly allied to Insects. The cucullus which covers the supposed mandibles would 

 have been considered the homologue of the labrum in Insects (in fact Westwood did describe 

 it as labrum, and Karsch named it clypeus), and a point of agreement between the two 

 classes as to the structure of the mouth would have been found in the fact that according 

 to their view the mouth was closed below, in both these classes, by a pair of limbs of 

 which the basal joints had coalesced into one plate whilst the following joints formed a pair 

 of palpi. 



7. Organs of Sense. 



All the known species are entirely blind. If eyes had existed in these animals they 

 would have been placed on the cucullus, but this part lacks every vestige of such organs. 



Our material for dissection was, as we have had occasion to mention more than once, 

 limited to one not full-grown specimen of Cryptostemma crassipalpe, but this we have carefully 

 examined with a view to the discover)' of such organs of sense, other than eyes — as are 

 known, particularly through the researches of Hansen (h), to exist in other orders of Arach- 

 nida. One of the antennae, one of the hindmost legs, and the abdomen were especially 

 examined for this purpose, after being cleansed by means of caustic potash. We did not, 

 however, succeed in finding here any of the so-called " lyriform organs," though these occur 

 in all Pedipalpi, both Amblypygi and the two tribes of Uropygi, on the antennae, the other 

 limbs, the cephalothorax and on all or almost all plates of the abdomen, and have been 

 discovered likewise in all other orders of Arachnida except Palpigradi. The examination of 

 Cryptostemma in this respect offered considerable difficult)- on account of the peculiar sculpture 

 and the covering of squamiform hairs, but we are confident of the correctness of our result, 

 that these organs do not occur in Cryptostemma. These Arachnida are likewise quite destitute 

 of those long, thin, tactile hairs, inserted in calicles, which Hansen has shown to exist in the 

 walking legs of Pedipalpi, and which besides are found on the large chelae of Scorpiones and 

 Chelonethi, on one of the pairs of legs in Palpigradi, and on the walking limbs of Aranese. 



At the same time we found on the upper surface of the last tarsal joint in each of 

 the three hindmost legs a very remarkable hair placed in the middle line, which we take to 

 be an organ of touch ; and it should be noted that we found it in Cryptocellus as well as 

 in Cryptostemma. On the two hindmost pairs of legs we found this tactile hair (PI. VII., 

 fig. 1 V, s) at a rather short distance from the terminal margin of the tarsus, which is 

 sinuate in the middle ; on the second pair of legs it is placed somewhat farther from the 

 margin. This hair is comparatively rather short (the specimen we have drawn has a length 

 of about 0038 mm.), cylindrical, slightly clavate, being a little thicker at the apex ; the two 

 distal thirds of its length are furnished all over with scattered delicate branches, which are 

 longer on the thicker terminal part ; but the almost semiglobular apex itself is bald. The 



