Effects of Destccati07j on the Rotifer 219 



another and a sort of telescoping of the body is thus permitted. 

 When fully contracted the head and tail are drawn entirely within 

 the large segment which covers the middle of the body and both 

 ends of the latter are puckered together as if drawn in with a string. 

 The animal in this condition is shaped like a lemon and is well 

 fitted to resist the injurious effects of desiccation. The part of 

 the cuticle that is outermost, that is, that which surrounds the 

 middle of the body, is thicker than the parts that cover the head 

 and tail. It is also somewhat different in chemical nature as is 

 shown by the fact that when living animals are placed in a weak 

 solution of methylene blue it is only part of the body that takes the 

 stain. This is true either of contracted animals or those that are 

 creeping or swimming. In the latter case a blue band appears 

 about the middle of the body, the head and foot remaining color- 

 less. The fact that that part of the cuticle which alone is exposed 

 at the time of drying -should be of a different nature from the re- 

 mainder is probably significant. Perhaps it may be more imperme- 

 able to water and thus check the rapidity of evaporation. Whether 

 or not it is a complete protection will be considered in another 

 place. Within the cuticle and the hypodermis which secretes it 

 are found the muscles; these are especially well developed in Phil- 

 odina on account of its habit of contracting and extending the 

 body. They are both longitudinal and circular, the former serv- 

 ing to draw the head and foot together at the time of contraction 

 and the latter by exerting a pressure on the fluids of the body to 

 cause their extension. In a rotifer dried slowly enough to retain 

 its natural form, the position of these muscles may be observed 

 in the form of slight thickenings beneath the cuticle. 



The various internal organs are much the same as those of other 

 rotifers. The mastax is well developed and the walls of the 

 stomach are thick and glandular. They usually appear more or 

 less yellowish, greenish, or sometimes a deep brick red, depending 

 on the amount of pigment present in the cells of Sphaerella on 

 which the animals are feeding. The nephridia are fairly conspic- 

 uous and under the higher powers of the microscope it is easy to 

 observe the peculiar flickering movement of the flame cells. A 

 contractile vesicle is present into which the nephridia discharge 

 their products. 



