ROTIFERS. 



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FLOSCULARIA TRIFOLIUM. 



aiiany it consists of a host of delicate filaments placed on a disc, which has, however, a circle of cilia on 

 its under edge ; or some fine tentacles may arise in a ring and be ciliated. Under all these conditions 

 the cilia and appendages can be withdrawn into the body by the longitudinal muscular fibres, 

 and also gradually everted. Moreovei', the animal itself withdraws down its tube if disturbed, and 

 comes forth again to a certain extent. There are usually, but not invariably, a stomach and mastax, 

 and in nearly all there are eyes. In one set of genera the rotary organ is flexuous and extended, 

 and has only one deep cut in. it ; and in the genus Megalotrocha the alimentary canal is singularly 

 developed, and there are two eyes. In another group the 

 rotary organ is entire, the genus Ptygura being the type. 



The genus Floscularia has the lobes of the rotary disc three 

 to six in number, has a tentacle-like proboscis at the side, and 

 the cilia on the rotary organ are of two kinds, some very long 

 .and excessively slender and comparatively motionless, and others 

 very small and not readily seen at the base of the long ones 

 on the inner side of the lobes. The number of lobes varies, 

 and five or six are commonest ; they are thickened at the free 

 margin. All the species make tubes of a delicate gelatinous 

 secretion, and live on the surface of the leaves and twigs of 

 Avater-plants. Melicerta ringens is a beautiful species of its 

 .genus, and is frequently found on water-plants, especially on 

 Potamogeton crispus. The rotary organs are four-lobed, and the 

 bodies are each in a tubular cavity. 



The young are very interesting on account of their 

 having a circular pre-oral disc, and two eye-spots, besides a 

 .second circle of cilia behind the mouth. Their shape, and 

 this distribution of rings of cilia, cause them to resemble the 



larvse of Annelida, and ally the class Rotifera very definitely with the Vermes. The genus 

 Lacinularia has a bilobed rotary organ deeply incised ventrally, and there is a double crown of 

 cilia. The individuals of a well-known species (Lacinularia socialis) unite, and remain fixed in the 

 midst of a gelatinous environment. 



Limnias ceratophylli, a form resembling the last somewhat, has only two lobes to its rotary organ, 

 l)ut its shell gets dark with age, from its collecting foreign bodies on it. It is a very typical form. 



The genus Stephanoceros has five tentacles, instead of lobes of the rotary organ, and they are 

 ciliated. It uses them to clasp its prey, and the body is attached by the base to a transparent 

 carapace. The length of Stephanoceros eichhornii is -^th of an inch. 



The genus (Ecistes probably comes into this family, and one species which has been studied by 

 Mr. Hudson makes pellets of its faeces, and piles them up gradually as a wall to its gelatinous tube. 



In considering the classificatory position of the Rotifera, the segmented condition of the body, the 

 presence of a water system and perivisceral cavity must be remembered. The nature of the mastax and 

 the rudimentary organs of special sense, the method of locomotion of some, and the tube-making of 

 others should not be forgotten. And when these very characteristic peculiarities of the Vermes are con- 

 sidered, with the fact of the resemblance of some immature free-swimming Rotifers to the ciliated larvae 

 of some Vermes, the propriety of placing the class in that great group must be admitted. The 

 Rotifera are not Infusoria, for their ova undergo a development not noticed in that group. Some 

 minute worm-like animals, with a rounded head and ten or eleven segments, the last of Avhich is 

 forked, which belong to the genus Echinoderes (Dujardin\ seem to link some of the Rotifera to the 

 lower Crustacea. They are marine, have no limbs, but the body segments have paired setse, and the 

 head has recurved hooks. The nervous system is a single ganglion, and has eye-spots on it. Moreover, 

 ^ Rotifer of the genus Pedalion (Hudson) has jointed setose appendages. 



CLASS NEMATHELMINTHA THE ROUND AND THREAD WORMS. 



A host of worms, mostly parasitic within man and the lower animals, and a few leading a free 

 life, belong to this class. All have cylindrical unjointed bodies, which are, however, marked with rings, 

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