WORMS. 



203 



tremity. This false foot or tail is jointed, and can be contracted and extended like a 

 telescope. It does not form a direct prolongation of the end of the body, but arises 

 from and is situated upon the ventral aspect. In most wheel animalcules there are 

 two eye specks, which are usually reddish in color. The oesophagus is provided with 

 a complicated masticating apparatus, the so-called " mastax," which is very interesting 

 to the anatomist. Such are the general characteristics of the group. 



The class was formerly confounded with the chaotic assemblage of minute 

 creatures, to which the name of infusorial animalcules was applied rather for conve- 

 nience than from discrimination ; but, says Rymer Jones, " the information at present 

 in our possession concerning their internal structure and general economy, while it 

 exhibits, in a striking manner, the assiduity of 

 modern observers and the perfection of our 

 means of exploring microscopic objects, en- 

 ables us satisfactorily to define the limits of 

 this interesting group of beings, and assign to 

 them the elevated rank in the scale of zoologi- 

 cal classification to which, from their superior 

 organization, they are entitled." The ciliated 

 lobes at the anterior end of the body have 

 given the class its name ; yet there are forms 

 known in which the cilia are wanting and the 

 lobes are excessively modified in shape. This 

 is notably the case in the parasitic genera Al- 

 bertia, Salatro, Seison, etc., which form the 

 family of the Ateocha (wheelless), and also in 

 certain species not parasitic. Of the latter, the 

 best known is a rotifer, described in 1857 by 

 the distinguished veteran among zoological in- 

 vestigators. Professor Leidy of Philadelphia, 

 under the name of Dictyophora vorax. This 

 rotifer is now united with several other allied 

 species in one genus, Apsilus. Apsilus vorax 

 is spheroidal, has no jointed tail, but is sessile. 

 Instead of the ordinary rotary discs it pos- 

 sesses a large protractile cup or disc. The 

 animal has the power of turning upon its point 

 of attachment, but does not appear to have the 

 power of letting go its hold. The animal is about one twenty-fifth of an inch long ; in 

 shape ovoid, the narrower pole being truncated and bearing the mouth. The body is 

 transparent, colorless, and even, and exhibits no signs of annulation, nor does it become 

 transversely wrinkled by contraction. The interior exhibits the digestive apparatus 

 and other organs, mostly more or less obscured by an accumulation of eggs in various 

 stages of development. From the truncated extremity of the body, the animal pro- 

 jects a delicate membranous cup, forming more than half a sphere and more than half 

 the size of the body. At will the cup is entirely withdrawn into the body, but, when 

 protruded, expands outwardly like an opening umbrella, and is the substitute for the 

 ordinary trochal discs of rotifers, and appears a most efficient means in catching the 

 animalcules which serve as its food. 



. — Apsilus vorax. 



