130 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL.97 



cases is far from evident, and the development of the mysid antennal 

 gland seems better explained as a secondary modification of the 

 developmental processes that give rise to the coxal glands of Arachnida 

 and the nephridia of Onychophora. 



Most of the tracheate Mandibulata have a series of head glands 

 pertaining to the gnathal somites, the openings of which lie mesad of 

 the appendage bases, or are displaced anteriorly or posteriorly when 

 the bases of the two appendages of a pair are united. Some of these 

 glands have been shown to have an apparent excretory function, 

 because of their property of eliminating from the blood particles of 

 carmine injected into the body of the animal, and such glands also 

 have a complex structure, usually described as consisting of a saccule, 

 a labyrinth, and a duct. Hence, various writers have claimed that 

 glands of this type represent nephridial organs corresponding with 

 the excretory head glands of Crustacea, though little evidence as to 

 their embryonic origin has been produced. 



The gnathochilarial glands of the Diplopoda have been shown by 

 Bruntz (1903) to collect injected carmine from the blood, and they 

 are said by Heathcote (1886) to be derived from the mesoderm in 

 embryonic development. Likewise, according to Bruntz (1908) and 

 Philiptschenko (1928), a pair of labial glands of apterygote insects 

 have an excretory function and a nephridialike structure. These 

 glands open either separately {Canipodca, Japyx) between the hypo- 

 pharynx and the labium, or {Machilis, Lepisuia) their ducts unite in 

 a common median duct, and are joined by the ducts of a pair of 

 "posterior salivary glands." The labial glands of the apterygote in- 

 sects, particularly those of Thysanura, would so evidently seem to be 

 the same as the labial glands of pterygote insects, which are commonly 

 found to be ectodermal organs, that it is difficult to believe they are 

 not homologous structures, regardless of their function. In the 

 Chilopoda, according to Fahlander (1938), there are present generally 

 three pairs of head glands associated with the bases of the gnathal 

 appendages, but in addition there is another pair having a complex 

 structure suggesting an excretory function. These glands have each 

 two openings, one mesad of the base of the first maxilla, the other 

 behind the base of the second maxilla. Fahlander contends, there- 

 fore, that each gland has been formed by the union of two nephridial 

 organs pertaining to the maxillary somites. The morphological status 

 of all such glands must yet be determined by a study of the embryonic 

 development. 



