294 



ROTIFER A. 



alimentary canal consists of oesophagus, mastax (chewing stomach), 

 glandular stomach, and intestine; all except the mastax cilated. 

 The mastax bears two chitinous jaws (trophi), which in life are in 

 constant motion and comminute the food. The cerebral ganglion 

 lies above the oesophagus, with which simple eyes and peculiar sense 

 organs, the cervical tentacles, are frequently connected. The 

 usually single ovary and the paired protonephridia empty into the 

 posterior part of the alimentary canal, which thus becomes cloacal 

 in character. For a long time males were unknown until Dal- 

 rymple discovered that these are much rarer and smaller ( dwarf 



Fio. 258. Brachionus urceolaris. A, female with four eggs in various stages ; B, male ; 

 C, 'flame' from protonephridia, greatly enlarged; b, urinary bladder; c, cloacal 

 opening; d, gastric glands; 0, ganglion, with eye; ft, testis; fr, mastax; TO, 

 stomach; o, ovary; p, penis; f, tentacle; 10, protonephridia. 



males/ and that they have a much simpler structure (fig. 258, #). 

 Usually the alimentary tract is reduced to a solid cord in which the 

 testes are imbedded. 



The Rotifers have two kinds of eggs, large winter eggs enclosed 

 in a thick shell and smaller thin-shelled summer eggs. The latter 

 develop parthenogenetically and by their numbers and rapid 

 growth subserve the distribution of the species. The winter eggs 

 require fertilization, and have a long resting period, thus serving 

 to tide over periods of cold or drought. The adult animals can 

 withstand a certain amount of desiccation; and they are often 

 found in damp moss or in eave troughs in a sort of sleep from 

 which they are awakened by water. 



