.8,,. NOTES ON ARACHNIDS. 525 



are generally regarded as the surviving representatives of a series 

 of nephridia, whicli formerly occurred in nearly all the segments, as 

 in many worms and in PcvipaUis. Lebedinsky has recently (g) de- 

 scribed the development of these glands in the common harvestman 

 {Phalangium opilio) in the embryo of which they open behind the first 

 pair of legs. Each consists of a coiled tube with thin walls opening 

 to the exterior by a straight duct with thicker walls. This duct, as 

 well as the glandular portion, is of mesodermal origin, being formed 

 by evagination, not, as in nephridia generally, by invagination of the 

 ectoderm. At present, Lebedinsky prefers to call these coxal glands 

 of Arachnids, and the shell- and green-glands of Crustaceans 

 " homodynamous " rather than " homologous." 



Passing from embryology, we have, in the work of Gaubert (i) 

 already referred to, an important contribution to the minute anatomy 

 of adult Arachnids of various orders. A comparative review is given 

 of the chitinous integument, chitinogenous layer, glands, sense organs, 

 appendages, locomotion, and influence of turgescence on the move- 

 ments of joints. Gaubert has only observed two layers in the cuticle, 

 and consequently doubts the existence of the third (intermediate) 

 thin layer described by Schimkewitsch. He has made experiments 

 on the cause of the rupture of the cuticle when it is cast, and has 

 produced artificial ecdysis by plunging spirit-specimens of spiders 

 into boiling water, concluding from this that the rupture is simply 

 due to mechanical pressure caused by the increased size of the animal. 



Elongated cells with large nuclei, occurring in the hypoderm of 

 the jaws, and believed by some former observers to be nervous, are 

 stated by Gaubert to be glandular, and to secrete a sticky fluid which 

 mixes with that from the maxillary glands ; similar cells occur on the 

 lower lip, and in the pharynx. Glandular cells also form the hypo- 

 derm at the base of the femora in Phalangium. The two layers of 

 the cuticle and the hypoderm are continued inwardly into the tendons, 

 and outwardly into the hairs, spines, and claws ; so that all tlie three 

 latter have a similar structure. This fact should prove consoling to 

 beginners in Arachnid classification, who may be often puzzled to 

 decide whether a certain excrescence is a " hair " or a " spine." 



Gaubert devotes much space to the " lyriform organs" on the 

 cephalothorax and limbs of Arachnids. These consist of series of 

 fine slits in the cuticle with central circular enlargements, filled by 

 thin bands. A number of these slits side by side give somewhat the 

 appearance of a stringed instrument, hence their name. They were 

 discovered on spiders by Bertkau, and now Gaubert has found them 

 also on spider-scorpions, harvestmen, and pseudoscorpions. He 

 gives very full descriptions of their numbers and position on the 

 numerous forms he has examined. From the enlargements of the 

 thin bands nerve fibres pass inwards, which lead to large nerve-cells, 

 whence fibres pass on to the nerve-trunk. The function of the 

 lyriform organs was believed by Bertkau and otliers to be auditory. 



