356 LOUIS MAX HICKERNELL. 



organs are arranged in the contracted animal. While in the 

 extended animal there are spaces between organs, when con- 

 traction takes place every available bit of space inside the trunk 

 integument is filled by the closely packed organs. The head and 

 foot segments are drawn entirely within the trunk by means of 

 the contraction of longitudinal muscles. The circular muscles 

 at each end of the trunk may then contract and cause the entire 

 animal to assume a shape not unlike a lemon. The large organ 

 systems can be seen through the integument of the contracted 

 rotifer. The head and its accessory structures can be seen just 

 anterior to the stomach tissue. The stomach occupies the 

 central part of the mass and is flanked on either side by the 

 reproductive organs. In the posterior end of the trunk the foot 

 segments containing the pedal glands can be seen. Fig. 4, 

 Plate II., shows a Philodina which has been contracted but is 

 just beginning to unfold. The foot segments are slightly pro- 

 truded while the head still remains within the trunk cavity. 



D. The Dried Animal. When the drop of water surrounding 

 a Philodina begins to dry up the animal indulges in active creep- 

 ing movements until the drop becomes too small to permit 

 further activity. The rotifer then contracts and actual desic- 

 cation begins. It is at this time, according to the older authors, 

 that the jelly membrane is secreted. The shiny appearance 

 described by them is indeed apparent at times but this is due not 

 to any jelly but to the fact that the tissues of the rotifers become 

 packed together as water disappears and since loss of trans- 

 parency accompanies loss of water the light is reflected rather 

 than transmitted by the animal. Final proof of the absence of a 

 jelly layer in dried rotifers w r ill be given in the part dealing with 

 sections. 



The internal organs cannot be carefully studied while the 

 drying is going on since the integument usually folds and wrinkles 

 as soon as drying begins. This obscures the internal structures. 



Animals dried under favorable conditions all tend to assume a 

 similar shape. The head and foot segments are drawn into the 

 trunk as before described. The circular muscles at the end of 

 the trunk contract giving to the animal a spindle shape. When 

 the drying process is very slow the irregular wrinkles do not 



