Development o/'Rotifer vulgaris. 129 



In Rotifer, as in the other Philodineae, the buccal aperture 

 is ventral, and the anal opening dorsal. 



The reception of nourishment is effected by means of the 

 so-called " rotatory organ," from which the whole group of 

 animals has obtained its name. In Rotifer this organ consists 

 of two lobes, situated before the mouth and directed outwards 

 like wings, which bear a strongly vibratile circlet of cilia, 

 and have the office of whirling in nutritive material. The 

 optical impression received by the observer of the incessant 

 ciliary movement is that of two rapidly revolving wheels, and 

 hence the name of "Wheel-animalcules" applied to them. 

 This organ, which can be protruded and retracted at pleasure 

 by the Rotifers, forms the true cephalic extremity ; and the 

 vermiform anterior third of the body, which bears the car- 

 mine-red eye-spots, may justly be regarded as a proboscidi- 

 form elongation. When the rotatory organ is retracted, a 

 system of radiately arranged folds indicates the place where 

 it is hidden in the body-cavity. When it is to be protruded, 

 the animal shortens its anterior extremity about one half, and 

 throws it quite back upon the neck, much as shown in fig. 2. 

 During this sudden backward movement the border of the 

 rotatory organ issues, already vibrating, and the motor muscles 

 of the latter protrude the two " prseoral lobes " completely. The 

 play of the cilia begins immediately, and numerous swarm- • 

 spores of Algse, Diatomacege, Infusoria, &c. are carried down 

 into the oesophagus, which is also lined with cilia. 



This latter leads into the so-called pharynx [mastax], 

 which contains the two denticulated jaw-plates, and possesses 

 a strong apparatus of muscles. When the rotatory organ is 

 unfolded these plates are in constant movement and ready to 

 crush whatever comes within their reach. By the older ob- 

 servers (Leeuwenhoek, Joblot, Fontane) the masticating ap- 

 paratus of the Rotifera was erroneously regarded as a heart. 

 If we examine a specimen of Rotifer, lying with the ventral 

 surface upwards, under a microscope of good definition with 

 a power of 750 diameters, we see the lower surface of the 

 pharynx, which is turned towards us, furnished with three 

 gland-like appendages. The third and largest one pushes itself, 

 like a wedge, between the two smaller ones, which converge to- 

 wards one another, and thus is produced a glandular complex 

 which occupies the whole lower surface of the pharynx. Eck- 

 stein (I. c. p. 445) thinks that in Rotifer and Philodina no 

 separate lobes are to be distinguished in the glandular mass. 

 I can explain this statement, wdiich differs completely from 

 the results of my own observations, only by supposing that 

 the Giessen observer has examined the pharynx of a Rotifer 



