NO. 6 ANNELIDA, ONYCHOPIIORA, AND ARTHROPODA SNODGRASS I29 



coelomic ducts of Onychophora. Brauer (1895) has shown that in 

 the embryonic development of the scorpion there are formed five pairs 

 of diverticula from the coelomic sacs of somites III, IV, V , VI, and 

 VIII, respectively, of which those of the fifth and eighth somites 

 acquire openings to the exterior. The coelomic sacs and their diver- 

 ticula in the fifth somite develop into the definitive coxal glands, the 

 coelomic diverticula of the eighth somite become the genital ducts, 

 and the sacs and diverticula of the other segments disappear. Accord- 

 ing to Kishinouye (1894) the development of the coxal glands in 

 the araneid genera Lycosa and Agelena shows that each organ is a 

 composite structure formed of small parts of the coelomic sacs of 

 somites ///, IV, and V, but only the first acquires an opening to 

 the exterior. 



The nephridial glands of the Crustacea, being individual organs, 

 resemble the simple nephridia of the Onychophora rather than the 

 composite coxal glands of the Chelicerata. Each organ consists of a 

 mesodermal end-sac, a mesodermal canal, which may become highly 

 complex in form, and a short exit duct of ectodermal origin (see 

 Cannon and Manton, 1927, and Manton, 1930). The embryogeny of 

 the crustacean excretory glands, however, is in some cases compli- 

 cated by an indirect course of development. 



The antennal gland of Hemimysis lamornae is said by Manton 

 (1928) to be formed from two masses of cells derived from the 

 antennal mesoderm, one of which produces the end-sac, the other the 

 canal. The canal becomes attached distally to the ectoderm, and a 

 small ingrowth from the latter forms a short ectodermal exit duct. 

 Where the canal touches the wall of the sac, a compact group of 7 

 or 8 cells bulges into the lumen of the canal, and at this point the sac 

 and the canal become united, but the only visible communication 

 between them, Manton says, is by fine rather vague channels passing 

 through the nephrostome cells. According to Vogt (1935) the an- 

 tennal mesoderm of My sis relict a produces only the canal and a sheet 

 of connective tissue membrane in the base of the antenna, to which 

 the canal becomes attached. A group of 8 cells in this membrane 

 then forms the nephrostome. The true end-sac, Vogt claims, is con- 

 structed from adventitious connective tissue cells that wander into 

 the antenna from the thoracic segments and form the end-sac beneath 

 the nephrostome membrane. Vogt contends that the development of 

 the antennal gland of Mysis relicta so closely resembles the develop- 

 ment of an annelid nephridium that the two organs must be homolo- 

 gous structures, the nephrostome membrane of Mysis representing 

 a dissepiment in the annelid. To the writer a parallelism in the two 

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