USE OF THE MICROSCOPE IN ZOOLOGY. 45 



the reproductive apparatus ; but in the wheel-animal- 

 cule, and other Rotifers, you will see a differentiation 

 of parts and a specialisation of organs. There is evi- 

 dently an integument or skin through which certain 

 viscera or internal organs can be discerned ; one of 

 the most conspicuous organs is what is sometimes 

 badly named the gizzard. This piece of organic 

 machinery, consisting of strong muscular substance, fur- 

 nished, according to the species, with various pointed 

 teeth, seems in these animals to be always going \ its 

 function is manifest even at a glance. You will notice 

 that various substances, drawn down in the vortex 

 caused by the action of the cilia, pass through this 

 manducatory organ, which, like a pair of miniature 

 mill-stones, grinds the food as it passes between them. 

 You will often notice both eggs and young ones 

 within the bodies of the wheel-animalcules, and very 

 curious it is to see under the microscope the move- 

 ments and contortions of a restless embryo rotifer. 

 The Rotifera possess, moreover, an intestinal canal, 

 a water-vascular system, and longitudinal muscles. 

 There is much difference of opinion as to their 

 proper place in the zoological scale. Some naturalists 

 think that these wheel-animalcules have their affinities 

 with worms, others with crabs. 



You will be almost in ecstacies of delight at first 

 becoming acquainted with the Melicerta ringens, an 

 exquisite little creature, pretty common in pools and 

 ditches, where it may be found sometimes in extra- 

 ordinary profusion, attached to the stems and leaves 

 of various aquatic plants. The Melicerta is a worm- 

 like creature, about as thick as a horsehair, and the 

 twelfth part of an inch in length^ It is itself the 

 architect of a very pretty little tubular house in which 

 it dwells. You should try to make the acquaintance 

 of Melicerta, for in the whole aquatic world there is 



