ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 989 



Foot-glands of Insects.* — In a careful research Heir J. Dahl 

 discusses the interestiug problem of the climbing of insects on smooth 

 surfaces, and reports the varied arrangement of foot-glands, hairs, &c., 

 in different groups. Among beetles (e. g. Superda) the attaching 

 hairs are seen to be but slightly modified cbitinous hairs exi^anded at 

 the lower end. Interiorly the hollow hair-tube is filled with a very 

 spongy cbitinous mass, which is limited at the expanded end by an 

 extremely fine membrane. The upper surface of the terminal exjDansion 

 is very generally beset with small hairs or warts, and the occurrence 

 of a single wart is apt to be mistaken for an opening. Even the 

 much modified sexual suckers of male Carahidse, Dytiscidse, &c., are 

 shown by transitional series and even by the minute homologies of 

 their structure to be nothing more than ordinary cbitinous hairs, 

 variously modified and strengthened by the occurrence of internal 

 rods and external folds or knobs. 



In connection with the attaching hairs there are marked cells 

 productive of a secretion different from tbe blood ; these cells form 

 the foot-glands. Between each hair and the gland which supplies it, 

 there runs a canal which enlarges slightly just at the root of the hair 

 and divides into as many (2-4) branches as there are supplying cells. 

 Besides the cells furnishing the attaching secretiou of tbe hairs, there 

 are in the Coleoptera abundant skin-glands present all over the body 

 as well as on the feet. They are probably analogous to sebaceous 

 glands, and unlike the former open directly to the exterior between 

 the hairs. The attaching glands originate from connective tissue 

 cells with the exception of the copulatory suckers of some Coleoptera, 

 which seem to arise from the matrix. Besides the (1) glands or 

 foot- glands proper and the (2) skin-glands, a third kind of glandular 

 cell is frequently present, e. g. in Feronia. These occur towards the 

 upper surface of the foot imbedded in the matrix, and have no canal. 



In the other orders of insects the foot-glands are all formed from 

 the modified matrix. The whole of the modified portion forms to a 

 certain extent a single gland instead of each cell acting independently. 

 In the Orthoptera the gland lies on the sole of the foot, which thus 

 acts as attaching organ ; in the Biptera it lies in two special attaching 

 lappets ; in the Hymenoptera and Lcpidoptera it lies above the claw- 

 bending sinew in the last joint of the foot, while the attaching organ 

 has the form of a lappet between tbe claws. 



As regards the actual physical process, Dahl maintains (1) that 

 an adhesive fluid is exuded from the glands; (2) that this is 

 different from the blood, containing probably a larger projiortion of 

 fatty stuff; (3) that the attaching hairs have delicate, soft-skinned 

 ends ; (4; that the quantity of fluid between the end of tbe hair and 

 the smooth surface to be climbed on is generally very slight ; (5) that 

 while there is also adhesion and cohesion the chief process may be 

 best described as capillary attraction. 



Morphology of the Mouth-organs of Hymenoptera. f — M. J. 

 Chatin comes to the conclusion that, even if the gnathitcs of the 



• Arch. f. Mikr. Aiiat., xxv. (188.5) pp. 2:5G-G3 (2 pis.), 

 t Coiiipti.K Ki,ii(Ui.-j, ci. (1885) pp. 2.59-01. 



