Ill 299 



Microcodon clavus Ehrbg. 

 Gosse 1889, p. 119. 



Gösse (Hudson-Gosse 1889, p. 119) supposes he has seen the male. 



"A female had been playing in my live-box within an area formed bj' bounding filaments 

 of Myriophylliim. Presently I saw a slender worm, about as long as this charming siil)ject 

 itself, of almost aerial transparency, very slender, darting about tlie same limited area. It was 

 a nearly perfect cj'linder, but gradually tapering to an acute extremity, which may possibly 

 have been a minute conical toe. The front, slightly bent downward, was transverselj' truncate; 

 its circular margin carrying a wreath of locomotive cilia, by whose vibrations it shot vigor- 

 ously and rapidly about. The whole body was refractive of light, but one vesicle, situate about 

 two-thirds from the front was more intensely refractive. This I suspect to have been the 

 sperm-sack. I could detect no other organ or visens in the animal, but the entire length and 

 breadth was full of minute granules." Gosse further supposes that he did indeed observe the 

 male, because the motions exactly resemble those of the female, because it appeared at the 

 same time and in the same dip. In support of his supposition he also emphasised the ap- 

 parent attention, which the supposed male paid to the female. 



Microcodides robustus (Glascott). 

 Tab. VI, fig. 1—2. 



Description. Body about twice longer than broad, sackformed behind ; cross sec- 

 tion almost circular. The forepart of the body rather sharph' defined from the broader 

 hindpart; cuticula thin, very hyaline. Foot remarkably strongly developed, almost 

 more so than in the female, but only with two joints; ventrally placed two rather 

 blunt short toes. Wheel-organ resembling that of the female, but the cilia as far 

 as I have been able to see, form a closed wreath round the somewhat obliquely 

 placed disc; upon this a few faintly developed elevations, carrying bunches of long 

 cilia. Below the hypodermal cells the large brain with a red eye below. Dorsal 

 antennæ two, situated near each other, united in a dorsal organ; two lateral 

 antennæ far behind. There are four conspicuous transversal muscle-bands; of longi- 

 tudinal bands three or four dorsal bands and two ventral ones; some of them are 

 deeply cleft. There is a conspicuous, but rather narrow rudiment of the alimentary 

 canal, embracing the testis; the lateral canals are very conspicuous, furnished with 

 three vibratile tags each. No contractile vesicle has been found. The testis is large, 

 pyriform, suspended in a very hyaline indusium of a similar structure to that which 

 is found in Hydatina; there are two sorts of spermatozoa; two small prostata glands. 

 Peculiar are the two liighlj' developed footglands, ending at the tip of the toes. The 

 opening for the testis is situated dorsally over the first footsegment; the penis seems 

 to be rather short, protrusile, the opening is surrounded by a wreath of cilia. Size 

 of female 6 — 700 /<,, of foot 250. Size of male 160 ,«. 



It is only with the greatest hesitation that I refer this peculiar male to the 

 genus Microcodides, but of all known Rotifers I cannot find any which it resembles 

 more than the female of Microdides rohiistus described by Glascott (1892) and later 

 on figured and redescribed by Rousselet (1895, p. 3). 



In May 1921 I found, in a little pond near Hillerød, a large, slowly swimming 

 Rotifer with sharply defined, ventrally placed strong foot; (he mastax was very pe- 



