ANIMAL NATURE OF DIATOME^E. 455 



which we have adverted in many species, seems to me to 

 prove what might easily be deduced from the ob- 

 servations of Ki.itz.ing that the so-called Spermatia are 

 developed within the fronds, if we may use an expression 

 taken from the vegetable kingdom.. I could never per- 

 ceive that these smaller Naviculse were included in 

 distinct tubes, or that they constituted an uniform series 

 in the order of their size. It seemed, rather, to be con- 

 stantly the case that they were dispersed through the 

 tubes of the larger ones. From this it seems that we 

 may conclude that when the spermatium is mature, when 

 its envelopes are broken up and about to be reabsorbed, 

 the young Naviculse, passing from tube to tube, are finally 

 dispersed. And continuing to supply the want of sufficient 

 observations by induction, we may suppose that these do 

 not begin to divide until they have attained their greatest 

 dimensions. It then becomes intelligible how the partial 

 tubes originate, through the persistence of the thin external 

 membrane, which we know, by preceding observations, 

 manifests itself distinctly whenever the deduplication 

 takes place. Only we must suppose that the silica is re- 

 absorbed, while the membrane remains in Monnema, 

 on the contrary, it disappears. It is most important to 

 observe how these series of Naviculse are formed within 

 the proper tubes. It is, in fact, the result of observation 

 that their disengagement is always effected in the plane of 

 the primary surfaces. The series may present either the 

 primary or the secondary surfaces. In either case the 

 Naviculse may be found arranged one behind another, 

 either contiguous or more or less apart. They are some- 

 times imbricated with the primary, never witli the se- 

 condary surfaces ; and when the imbricated series is 

 viewed on one side, the Naviculse present themselves 

 with then- secondary surfaces entirely free and inclined 

 obliquely. Therefore we must suppose, so soon as the 

 deduplication (sdoppiamento) has taken place, the two 

 new individuals, rotating upon one of the sides of their 

 surface of contact, as upon a hinge, represent, in some 



