430 ANIMAL NATURE OF DIATOMEiE. 



confused within ; but in some others it seems as if 

 instead of a tube there is a mucous mass in which the 

 Naviculse are immersed. Then there remains a doubt 

 whether the series of these Naviculse are included in 

 distinct tubes or in simple canals hollowed out of the 

 common mucous mass. It may perhaps be suspected 

 that the tubes visible in specimens that have been 

 moistened, do not really exist during life, and originate 

 in a change that has taken place after death. And it is 

 quite certain that the partial tubes waste away sometimes, 

 as well during life as by some alteration happening after 

 death, so that they appear evident in some but not in 

 other parts of the same specimen. The character indi- 

 cated by Kiitzing of the so-called spermatia, external 

 in Monnemce [Schiconema, Kiitz.), and internal in Schizo- 

 neincE {Ilicromega, Kiitz-.), would therefore assist us very 

 much, were it constant and capable of being verified. 

 But Kiitzing himself only found these spermatia external 

 in a single species {S. tenue). Therefore there only 

 remains the sole negative character of the absence of 

 partial tubes, and whenever we succeed in observing 

 these, the species must undoubtedly be referred to the 

 succeeding genus. The absence of partial tubes, and 

 consequently confused disposition of the Naviculse, is 

 evident in the following species. 



Monnema quadripundatum, Grev. 



Kiitzing changed Lyngbye's specific name {Bangia 

 quadripundata) as erroneous, and substituted that of 

 Sdiizonema tenelluni ; establishing the length of the 

 Naviculae, from Lyngbye's original specimens, to be 

 ■^" , which, in the Paris line, would equal 00235 milHm. 

 But, with an ampUfying power of 420, he represents it no 

 more than 5'5 millim., which is equal to 001 31 millim. 

 Estimating this line conventionally at 2 millim., yijth of this 

 would be 0-017 millim., and there would be more agree- 

 ment. But upon an original specimen with the same 

 name he establishes another species (^S*. Ekrenbergii) 



