128 Dr. 0. Zacharias on the Reproduction and 



Hcematococcus pluvialis and Stephanosphcera pluvialis, must 

 certainly be well known to a wide circle of naturalists. The 

 last-mentioned interesting Volvocinean occurs in great abun- 

 dance in the stagnant water of this ditch. 



At almost all seasons the Froschgraben possesses an abun- 

 dant fauna. Besides numerous species of Chironom ws-larva?, 

 Cyclopidse, Entomostraca (Lynceus), Nematoda, and Infu- 

 soria, three different species of Kotatoria are to be found here, 

 viz. : — 



1. Philodina roseola. 



2. Eosphora najas. 



3. Rotifer vulgaris : 



(a) in a very large form (0 - 75 millim.), with reddish 



cuticle ; 

 (ft) in a smaller form (0*50 millim.), with perfectly 

 colourless cuticle. 

 As I needed a great number of specimens I have experi- 

 mented with the smaller Rotifer ; the other two species did 

 not occur in sufficient abundance, and I employed them chiefly 

 only to obtain a more accurate notion of the characters of the 

 Rotatorian organism. I found the large Rotifer cited under 

 "3a" specially adapted for this purpose ; from its sha- 

 greened cuticle it might be characterized as Rotifer granulans. 



III. The Anatomy of Rotifer vulgaris. 



The external boundary of the bilaterally symmetrical body 

 of our Rotifer is formed by a finely longitudinally striated, 

 transparent cuticle, the interior, softer portion of which (hypo- 

 dermis) consists of a homogeneous ground-mass with scattered 

 granules. Leydig, who was the first to notice the existence of 

 this second layer, describes it as the granular layer. The 

 telescopically extensible foot (like the cervical process or pro- 

 boscis) is to be regarded as merely an extension of the cuticle, 

 not as an organ articulated to the latter. Division into 

 segments, in the sense in which it occurs in the Arthropoda, 

 is no more to be discovered in Rotifer than in the other 

 Rotatoria. By this, however, it is by no means intended to 

 deny that a sort of superficial segmentation divides the body 

 in the Rotatoria into several segments placed one behind the 

 other ; this is undeniably the case, but no metamerous ar- 

 rangement of the internal organs corresponds to these apparent 

 segments. Butschli therefore has rightly come to the con- 

 clusion that the jointing of the Rotatoria is typically different 

 from the segmentation of the Annelida*. 



* Zeitsclir. f. wiss. Zool. xxvi. (1876). 



