1891.] Zoology. 281 
same segment and has its openings at the base of the second maxille. 
The fourth and fifth systems are very similar in structure, but differ in 
the position of their ducts. The fourth opens just behind the second 
system, the fifth goes through the body wall immediately behind the 
commissure uniting the dorsal and supraneural vessels. The histology 
and structure of these systems are detailed. Regarding the functions of 
these glands Herbst has but little to offer. He thinks that some of 
them (possibly System III.) may act as spinning glands; while others 
may play a part in preparing food material. A discussion of the 
homology of these glands with the head glands of Hexapods and the 
coxal glands of other Arthropods follows, but our knowledge of these is 
not sufficient to lead to sure results, though the author considers them 
as homologous with the coxal glands. 
The circulatory apparatus is also described, the most interesting 
features pointed out being the existence of a cardiac nerve, arising 
probably from the sympathetic ; and the comparison of the supraneural 
vessel and the arteries on either side of the cesophagus with the similar + 
organs in the Annelids. 
The Balancers of Diptera.—Ernst Weinland presents a long and 
detailed account * of his studies of the balancers or halteres in twenty 
genera of flies. The position, color, hairs, relations, the chitinous 
skeleton, internal structure, canals, terminal vescicle, nerves and nerve- 
end structures are’ described at great length and illustrated by five 
plates. The results may be summarized ina few words. The balancers 
are to be regarded as extremely modified wings with internal canals 
corresponding to those in the ‘‘ veins’’ or ‘¢nervures’’ of the true 
wings. They have not yet lost their powers of motion, a hinge remain- 
ing at the base, and in accordance with their position the direction of 
the flight of the fly is changed. The sense organs with which they are 
clothed must be regarded as organs of equilibrium. 
Nerves of Tortoise Shell.—J. B. Haycraft has noticed the 
_Sensitiveness of the carapace of the land tortoise (Zestudo greca) of 
Southern Europe. He finds that nerve-fibres penetrate the osseous 
portion of the carapace and enter a connective-tissue layer immediately 
beneath the scutes. In this latter they lose their undulated character, 
and become covered with a dense sheath of tissue. With suitable prepa- 
3 rations these nerves are seen to branch, and the ultimate fibres can be 
traced to the nuclei of the epidermal cells. Not all cells are thus 
innervated, nor were any nerves found within the shell itself. 
* Zeitsch. f. wiss. Zoologie, LI., p. 55, 1890. 
