408 ANIMAL NATURE OF DIATOME^). 



in any other Diatomese, the stipes truly merits particular 

 consideration. Its constant collocation proves that the 

 Achnanthides are, like the Surirettce, adherent by one 

 extremity, and the insertion of the stipes becomes oblique 

 only because the duplication always takes place on the 

 side of the dorsum ; that is, in other words, from the two 

 individuals which are formed at the expense of the first 

 one, only the one corresponding to the dorsal surface is 

 ultimately separated; and the same thing occurs with 

 those that follow. As to the internal substance, Ehren- 

 berg says it is divided into many rounded portions, 

 which in A. lonyipes collect in the middle, like rays, 

 around the median aperture. In the A. salina (A. bre- 

 vipes, Ehr.) the same Ehrenberg describes this substance 

 as separated, from the first, into four lobes, which 

 finally divide and resolve themselves into moveable cor- 

 puscles. 



23. CYMBOSIRA. Individua vel solitaria vel binata, 

 stipitata ; in series isthmo yelineo concatenate. . 



The essential character by which the single species 

 (C. Agardhii) generally differs from the Achnanthides 

 seems to indicate that in this the duplication happens 

 promiscuously either in the inferior individual or the 

 superior. The series consisting of solitary individuals 

 may be considered as originating from the successive 

 duplication of only one superior or dorsal individual. 

 The same may be supposed of the series of geminate 

 individuals alternately conjoined; but when the con- 

 junction is unilateral the supposition is admissible that 

 after the first duplication is accomplished the second is 

 effected in an inferior individual, and repeated in the 

 inferior one through the successive links of the chain. 

 We may notice that the dimensions vary greatly in 

 different individuals, but are constantly the same through 

 all of one series. The specimens from Cayenne, para- 

 sitic on Polysiphonia subtilissima, (along with Podosyra 

 Montagmi and Odontella polymorpha,} differ from the 



