962 SUMMARY OF CURRENT RESEARCHES RELATING TO 



4. The granular material which fills the cone, or the non-nervous 

 portion of tho motor termination, exhibits nuclei varying in form 

 and number, in all the Arthropods noted with the exception of 

 Geophilu8. 



5. The branches resulting from tbe terminal bifurcation of the 

 axis never exhibit in their course strictly associated nuclei. 



6. With the exception of Blutfa, in all the other Arthropods 

 examined, there seoms to be only one elevation of Doyere for each 

 muscle-bundle. 



7. In Blatta and Oryctes tho motor nerve passes through a nerve- 

 cell before joining the muscle-bundle. In all the species examined 

 the nerve is frequently accompanied by a tracheal filament. 



Dermal Sensory Organs of Arthropoda.* — Prof. F. Leydig reminds 

 us that he has already exjn'essed the opinion that all such structures 

 as tactile seta?, olfactory bulbs, and auditory hairs of Arthropods are 

 modifications of the ordinary hairs and setae. The question naturally 

 arises, what are the contents of the ordinary hair-like processes of tho 

 integument? Sting-hairs, such as those on the larva of Saturnia, 

 have a wall, the structure of which is similar to that of the dermal 

 carapace. There is a homogeneous cuticle, a cellular matrix, and a 

 contained blood-fluid. Where the hair is articulated to the integu- 

 ment the lumen is either simply filled with clear fluid, or it is spanned 

 over by plexuses, in the meshes of which the fluid is contained. The 

 fluid contents appear to be of the nature of a secretion. In the larva 

 of Bombyx rubi there are multicellular pouches, and in that of 

 Dasychira f)udibunda unicellular glands. The cuticular wall of the 

 hair may be derived from the matrix cell ; the fluid within represents 

 the hyaloplasm of the cell-substance, while the plexus is derived from 

 the spongioplasm. 



The tactile setae are distinguished by being the support of the ter- 

 minal ganglionic cell of the nerves, and it is really in this point only 

 that they differ structurally from ordinary setae. The cylindrical or 

 conical bodies which have had an olfactory function assigned to them, 

 have a more special character. The extent of the cuticular invest- 

 ment varies with an aquatic or terrestrial habit, for in insects and 

 Myriopods the chitinous coat is of the same thickness along the whole 

 of the organ, while in the Crustacea it is much thicker at the base 

 than it is at the tip. Further, the free end of the bulb has an orifice, 

 and the contained substance is a pale homogeneous substance which 

 seems to be a naked axis-cylinder. 



The auditory rod is an enlargement of a nerve-tube. It has an 

 investment which is at first delicate, but which gradually thickens, 

 and is the cause of the dark margin. The clear homogeneous contents 

 correspond to the nervous hyaloplasma. 



Tactile setae may be scattered over the surface of the body of an 

 Arthropod, and are sometimes collected at definite jioiuts. These are 

 those which an observer of the living animal is inclined to regard as 

 gustatory organs ; indeed, tactile setae and gustatory hairs are not to be 



* Zool. Anziig., ix. (1886) pp. 284-91, 308-14. 



