160 Prof. J. Wood-Mason's MorpJiological Notes 



a film of liquid, the secretion of the gland, its microscopic 

 appearance being precisely that of an object examined 

 under the microscope before the spirit from which it has 

 been taken has had time to evaporate fi-om its sm-face, and 

 a minute drop of fluid being left upon a piece of glass 

 applied to it. In the worms the secretion of the segmental 

 organs is carried out of the body by cuiTcnts created by 

 the cilia with which the walls of the excretory canals are 

 clothed, but in Macliilis, and probably in Peripatus also, 

 by the eversion of the pouches, no arthropod possessing 

 cilia on any part of the body at any period of its existence. 



In the first abdominal somite the apertures of the glands 

 are placed much nearer to the middle line than elsewhere, 

 and it is clear that the ventral tube or sucker of the 

 Collembola (which bear much the same relation to the 

 Thysanura as the Brachyura do to the Macrura amongst 

 Crustacea, or as spiders to scorpions amongst Arachnida) 

 has resulted from the coalescence, or rather the partial co- 

 alescence, of this pair of glands, for it everywhere exhibits 

 traces of having once been a paired organ: — "In Podura, 

 Lipura and the allied genera, this organ is," according 

 to Lubbock,* " a simple tubercle, divided into two halves 

 by a central slit; in other genera, as, for instance, in 

 Orchesella and Tomocerus, the tubercle is enlarged and 

 becomes a tube, divided at the free end into two lobes. 

 In the SmynthuridcB and Papiriidce the organ receives 

 a still further and very remarkable development; from 

 the end of the tube the animal can project two long 

 delicate tubes, provided. at their extremity with numerous 

 glands." Similarly, the first maxillge in myriopods, and 

 the second in insects, have coalesced to form a labium, 

 different pairs of abdominal appendages, the springing 

 apparatus of the Collevibola, the originally paired sexual 

 apertures, the single aperture of all insects,f &c. 



The glandular pouches are absent fi^om the tAvo genital 

 somites in Machilis, having possibly united to form the 

 apertures and ducts of the genital and accessory genital 



* Lubbock, ' Monograph of the Collembola and Thysanura,' p. 68. 



■j- It is interesting to find in the lowest insects (Thysanura) traces of the 

 former duplicity of the sexual aperture. Meiuert says of lapyx, — " The 

 sexual orifice rests on the posterior margin of the ventral shield of the 

 eighth ring, and the deeplij bifid vagina of the female can be protruded 

 from the latter;" and of Campodea, — " The sexual orifice is behind the 

 eighth ventral shield, in a conical protuberance, which is simple in the 

 male, but in the female almost hifid." lajii/.v and Vampodca are in this 

 respect intermediate between the rest of the insects and the myriopods. 



