1 2 8 WHEELER. [Vol. V 1 1 1 . 



ments, be"-inning with the first. The solid testes show no 

 traces of metamerism. In the young Lepisma, according to 

 the same authority, the egg-tubes are also segmental, there be- 

 in"- five in either ovary, a pair in each of the five basal abdominal 

 seo-ments. In the adult this character is no longer noticeable. 

 In certain species of Lcpismina, there are six sacs in either 

 testicle, united in pairs on either side. These also lie in the 

 basal abdominal segments. " L'organisation segmentaire des 

 ovaires chez lapyx se repete chez Madiilis. Cette repetition 

 dans des formes tres eloignes I'une de I'autre comme le sont 

 precisement lapyx et Machilis, tend a donner au fait una 

 serieuse valeur morphologique. Les tubes ovariques de Machilis 

 sont au nombre de sept de chaque cote." In the latter form 

 Oudemans ('8?) also figures seven egg-tubes strung along the 

 oviduct, but without a clearly marked metameric arrangement. 

 In the male there are three pairs of testicular sacs. 



In all these Thysanura the female, as might be expected, ad- 

 heres more tenaciously than the male to the metameric scheme. 

 It will also be observed that the number of egg-tubes (five to 

 seven pairs) is about the same as the number of germ-cell clus- 

 ters in embryo Orthoptera. The position of the organs is also 

 identical, viz. in the first to seventh abdominal segments. We 

 might conclude, therefore, that the sexual organs of the higher 

 Thysanura represented an embryonic or arrested condition. 



A difficulty is encountered, however, when we stop to ask 

 the question : Is the individual egg-tube in such a form as Ma- 

 chilis homologous with an individual egg-tube in Blatta or any 

 other Pterygote } So far as structure is concerned, this would 

 appear to be the case. We should also say that each egg-tube 

 of lapyx or Machilis was a metameric unit. But the lowest 

 number of egg-tubes in the Blatta ovary is sixteen, and as this 

 is more than double the number of metameres which contribute 

 germ-cells in the embryo, the egg-tube in this form cannot be 

 regarded as a metameric unit. We must conclude, therefore, 

 either that the individual egg-tubes are not homodynamous in 

 the Pterygota and Apterygota, or that the ovaries in lapyx, 

 Machilis, etc., are not primitively metameric. The possibility 

 of there being an acquired metamerism, or pseudometamerism 



