PHILODINAD^E. 97 



All the Eotifera seem to possess the power of secreting a viscous fluid, which they 

 put to various uses. The Rhizota form their cases of it ; the Plo'ima and Scirtopoda 

 draw it out in long threads from spots to which they have adhered, and thus moor them- 

 selves to external bodies ; while the Bdelloida, by coating themselves all over with it, 

 not only resist the extremities of heat and drought, but set at defiance Old Time him- 

 self. 



Family III. PHILODINAD^E. 



Corona a pair of circular lobes transversely placed ; ciliary wreath a marginal con- 

 tinuous curve, bent on itself at the dorsal surface so as to encircle the corona twice, with 

 the buccal orifice between its upper and lower curves, and having also two gaps, the one 

 dorsal between its points of flexure, and the other ventral in the upper curve opposite to 

 the buccal orifice ; tropM ramate. 



The genera of this family resemble each other so closely that it has often been 

 suggested that they should be reduced to one. They differ from each other chiefly in 

 the number and position of their eyes. One genus has them at the free end of the 

 cylindrical frontal column which forms the anterior portion of the head ; and within 

 which, through a fold on its ventral side, the rotatory apparatus can be withdrawn. In 

 another genus they are placed within the neck ; while in a third they are entirely 

 wanting. Now, strong objections have been made, by Dujardin and others, to Ehrenberg's 

 use of coloured spots for the purposes of classification ; mainly on the ground that it is 

 not certain that they are really organs of sight : and it is true that, in many cases, there 

 is little else to be seen in these so-called eyes but an irregular spot of pigment. On the 

 other hand, some of the Kotifera have unmistakable eyes, consisting of a spherical lens 

 seated on a sort of red, black, or purple cushion. Nerve-threads too, in some species, 

 can be traced from the ganglion to the eyes ; and by this means the general positions 

 and appearance of coloured spots, that really are eyes, have been established. Moreover 

 (as might have been expected), the undoubted eyes prove to be in these cases good 

 generic characters. When, therefore, pigment spots are visible in positions that the 

 undoubted eyes usually hold, it is reasonable to consider them to be organs of vision 

 however humble, and to make use of them with other characters in classification. In 

 the genus Rotifer, nerve-threads may be seen passing from the ganglion to the eyes 

 in the frontal column ; and in Rotifer vulgaris Dr. Otto Zacharias has observed " that 

 each of the two carmine-red eye-spots is furnished with a crystalline body." Again, in 

 the genus Philodina the position of the red spots with respect to the nervous ganglion is 

 precisely that which is held by such unmistakeable eyes as those of Conochilus volvox. 

 1 have decided, therefore, to retain the old genera with only a few alterations. 



Genus PHILODINA, Ehrenberg. 



GEN. CH. Eyes two, cervical. 



The Kotifera comprised in the genus Philodina, though technically separated from 

 the rest of the family by their having two eyes in the neck, can be generally recognized 

 at a glance by their greater stoutness of build, by their larger heads, by their more 

 powerful wreaths, and by their habit of so contracting the foot as to form &n abrupt 

 division from the trunk. The corona and ciliary wreath would closely resemble those of 

 Limnias, were it not for the break in the latter just opposite to the buccal orifice, by 

 which the upper wreath is converted into two segments of circles. The animal, too, 

 holds itself differently from the Rhizota while it is feeding ; for it slightly arches the 

 dorsal surface so as to throw forward its dorsal antenna ; while the Rhizota (with the 

 exception of Cephalosiphon) reverse this, and arch the ventral surface so as to throw 

 forward the two ventral antennae. A Philodina or Rotifer, when creeping, shows no 



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