THYSANURA I 87 



All the Thysanura possess salivary glands. In Cainpodea 

 there are ahout sixteen extremely short Malpighian tubules, or 

 perhaps glands representing these organs ; Jajyyx is destitute 

 of these structures ; Macliilis maritima has twenty elongate 

 tubules ; in Lepisma also they are long, and apparently vary in 

 number from four to eight in different species. The propor- 

 tions of the three divisions of the alimentary canal differ 

 extremely ; there is a very large proventriculus in Zejnsma, but 

 not in the other families ; coecal diverticula are present on the 

 anterior part of the true stomach in Machilis and in Lepisma, 

 but are wanting in Campoclea and in Jupyx. 



The dorsal vessel seems not to present any great differences 

 in the sub-order. Grassi says there are no alary muscles present, 

 but Oudemans describes them as existing in Machilis, but as 

 being excessively delicate. 



The ventral chain of nerve-ganglia consists in Cainpodea of 

 one cephalic ganglion, one sub - oesophageal (which clearly 

 belongs to the ventral series of ganglia), three thoracic, and 

 seven abdominal. In the other families there are eight instead 

 of seven abdominal ganglia. 



The structure of the internal sexual organs is very remark- 

 able in the Thysanura. In Gctmpodea there is one extremely 

 large, simple tube on each side of the body. In Japyx there are 

 seven small tubes on each side, placed one in each of the suc- 

 cessive abdominal segments, and opening into a common duct. 

 In Macliilis there are also seven tubes opening into a common 

 duct, but the arrangement is no longer a distinctly segmental one. 

 In Lepisma there are five egg -tubes on each side, the arrange- 

 ment being segmental in the young state but not in the adult 

 condition. In Campodea nutrient cells alternate with the eggs 

 in the tubes, but this is not the case in the other families, 

 rig. 94 shows the ovaries in three of the Thysanura ; in the draw- 

 ing representing this part in Machilis (C), one of the two ovaries 

 is cut away for the sake of clearness. 



The male organs in Carnpodea are very similar in size and 

 arrangement to the ovaries, there being a single large tube 

 or sac and a short vas deferens on each side of the body. In 

 Japyx there is a sac on each side, laut it is rendered double by 

 a coecum at its base, and there are long and tortuous vasa 

 deferentia. In Lepisma there are three pairs of coeca on each 



