430 ANIMAL NATURE OF DIATOMEJ3. 



confused within ; but in some others it seems as if 

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

 Naviculae 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 Monnema (Schizonema, Kiitz.), and internal in Schizo- 

 nema (Micromega, 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 Navicufce, is 

 evident in the following species. 



Monnema quadripunctatum, Grev. 



Kiitzing changed Lyngbye's specific name (Banc/ia 

 quadripunctata) as erroneous, and substituted that of 

 Schizonema tenellum ; establishing . the length of the 

 Naviculse, from -Lyngbye's original specimens, to be 

 ji/", which, in the Paris line, would equal 0-0235 millim. 

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

 more than 5'5 millim., which is equal to - 0131 millim. 

 Estimating this line conventionally at 2 millim., -^th 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. Ehrenbergii} 



