ROTIFERS. 449 



have the power of retracting itself perfectly within tho 

 hyaline membrane. The hyaline membrane is at certain 

 periods of the year so very translucent that it cannot be 

 made out ; later in the season it is found studded with para- 

 sitic desmids, when its gelatinous form is readily seen. The 

 body is ovoid or cup-shaped, and the mouth is surrounded 

 by long cilia, which are always in rapid motion. When 

 the animal becomes alarmed it instantly retracts, and then 

 has the appearance of a small round ball. On the frontal 

 plane four thickish conical erect papillae are placed, each fur- 

 nished with one or more spines or sefoe ; very near their 

 base, rather behind, and between the division of the 

 ciliary band, are the very minute visual organs. The 

 jaws, it is said, are furnished with teeth, but these we 

 have not been able to make out, chiefly owing to their 

 disposition to break up in a short tune after being placed 

 in confinement. The stomach is oval, and two ovoid 

 bodies are observed near the termination of the oesophagus ; 

 below these the ova-sack encloses a single ovum of a dark 

 colour. The ovum is surrounded by spinous processes, or 

 cilia, and when first thrown off it lodges for a time in the 

 hyaline membrane ; but, when set free, moves slowly 

 about. A few minutes after being placed in the glass-cell 

 the colony become uneasy, break themselves off one after 

 the other, and swim away to die. They were formerly 

 classed among Volvocinece, but bear no resemblance to 

 them, except in their roll through the water ; and are 

 more properly placed among the Rotifers. 



Acineta tuberosa, Plate 111. No. 68. The researches of 

 Stein are said to prove that the several members of this 

 family are simply a developmental phase of Vorticellina; 

 this view, however, is controverted by Lachmann, Cla- 

 parede, ~nd others who have witnessed the reproduction of 

 Acinetce from parent forms. A. tuberosa has a triangular- 

 shaped body and three obtuso tubercles or horns, each 

 furnished with tentacula. Many other forms of this 

 genus are well known ; but, notwithstanding the diversity 

 in construction, Stein declares their tubular ramified pro- 

 cesses to be morphologically and physiologically identical 

 with ordinary tentacula. Vaginicola crystallina he puts 

 forward as one of the best illustrations to be obtained of 



G O 



