GR USTA GEA—INTEG UMENT—MUSGULA TUBE 



331 



homologous with the spinning and setiparous glands of the Annelida and the coxal 

 glands of other Arthropoda. 



In the basal joints of the 8 pairs of thoracic limbs of Nebalia hypodermal 

 glands have been observed ; it is probable that these perform excretory functions. 

 Their position recalls the leg glands of SrancMpus. 



We may here further mention — the dermal glands which occur in the basal joints 

 of certain limbs of the Fhronimidce ; and the beautifully consti'ucted dermal glands 

 in the limbs of the Gorophiidce ; the unicellular dermal glands scattered in various parts 

 of the body of Orchestia ; the scat- 

 tered dermal glands of the Anisopoda 

 ( Tanais, Apseudes) ; the hook glands 

 of Caprellidce ; and the so - called 

 cement glands of female Decapoda, 

 which lie on the ventral side of the 

 abdomen, and whose hardening secre- 

 tion serves for the attachment of the 

 eggs. 



In Tanais and the Corophiidce the 

 secretion of the above - mentioned 

 glands hardens in water, and prob- 

 ably helps, by cementing together 

 foreign particles, to form the tubes 

 inhabited by these animals. 



Special interest is claimed by the 

 uni- and multi-cellular dermal glands 

 lying scattered under the chitinous 

 cuticle of the Corycceidce {Oopepoda), 

 because in them the connection of 

 the gland cells with nerve fibres can 

 be easily observed. A unicellular 

 dermal gland with cuticular duct, 

 which opens through a pore of the 

 chitinous integument of the body, 

 is in the Corycceidce generally coupled 

 with a terminal ganglion cell lying 

 under a sensory seta. The nerve 

 which runs to this pair of cells divides 

 into 2 threads, one of which is con- 

 nected with the gland cell and the 

 other with the ganglion cell. 



Fig. 230. — Diagrams to demonstrate tlie 

 mechanism of the motion of the segmented body 

 In the Arthropoda. One larger segment (ct) and 4 

 smaller. The exoskeleton is denoted by black lines, 

 the interarticular membranes by dotted lines. The 

 hinges between consecutive segments are marked a. t, 

 Tergal (dorsal) skeleton ; s, sternal (ventral) skeleton ; 

 d, dorsal longitudinal muscles = extensors (and flexors 

 in an upward direction) ; v, ventral longitudinal 

 muscles=flexors. In B, the row of segments is 

 stretched ; in A, by the contraction of the muscle d, 

 bent upwards ; in G downwards, (ff, Tergal ; sg, 

 sternal interarticular membranes. 



III. The Musculature. 



A continuous dermo-mus- 

 cular tube, such as is character- 

 istic of the worms in general, 

 and specially of the Annulata, 

 is wanting in the Crustaceans, 

 and indeed in the Arthropoda 

 generally. The development 

 of the cuticular integumental covering into a much firmer exoskeleton 

 makes a greater localisation of the musculature possible. 



