306 Dr. 0. vom Rath on the 



found that, in a shiiihav way, the first three thoracic appen- 

 dages also, which are termed maxillipedes or accessory 

 maxillge, are richly provided with sensory hairs on the exo- 

 podites, endopodites, and lobes (first maxillipede). Owing to 

 the agreement shown by these discoveries I considered it 

 a priori probable that all the pairs of appendages belonging 

 to thorax and abdomen would have their sensory hairs. 



c. Sense-organs of the Thoracic and Abdominal 

 Ajypendajes {Pleopoda) . 



The presence of sensory hairs upon the whole of the extre- 

 mities 1 determined successively in the Phyllopoda [Branchi- 

 pus and Apus), Cladocera {Daj'hnia, Sida, Moina), Copepoda 

 {Diaptomus, Cyclops, Calanus), Amphipoda [Phroninia^ 

 Hyperia)^ Isopoda (Anilocra, C>/mothoa, Idothea), Schizo- 

 poda [Sit'iella, Mysis), and Decapoda [Astacus and Palmmon) . 

 In the case of biramose appendages, sense-organs are found 

 upon the exopodite as well as the endopodite. In the Cirri- 

 pedia (e. g. Lepas) I found that the whole of the hairs upon 

 the cirriform limbs were sensory. In the Arthrostraca and 

 Thoracostraca the abdomen consists, as we know, of seven 

 segments, of which the first six usually bear pairs of limbs 

 (pleopoda), while the telson, or seventh segment, is ahvaj^s 

 apodous. Even the telson is provided with sensory hairs. 

 1 cannot here enter upon a closer description of the sensory 

 hairs of the several appendages in the different families and 

 species. The auditory organs situated in the endopodite of 

 the last pair of pleopoda, the so-called tail, of the Schizopods 

 Siriella and Mysis are provided with otolithic hairs, 

 possessing the characteristic peculiarities described above in 

 the case of the auditory hairs of the first antennee. In the 

 Schizopods we also find free auditory hairs upon the surface 

 of the tail. 



d. Free Sense-organs upon the Segments. 



Under this head I merely make passing allusion to the fact 

 that in a few rare cases free sensory hairs have also been 

 described as existing upon the somites, and have been held to 

 be tactile in function. Weismann found feathered tactile 

 seta3 standing in pairs upon the dorsal surface of the fourth 

 abdominal segment of Leptodora, and Claus alludes to 

 similar free tactile bristles upon the somites of Branchipus. 



