AURELIA AURITA 41 



at its base and a small club or tentaculocyst under it. An oral ol- 

 factory pit is situated at the base of the tentaculocyst. The 

 tentaculocyst is hollow except at its end which is developed as a 

 statocyst or an organ of equilibrium and is filled with statolyths. 

 On the aboral surface of the tentaculocyst, a little in front of the 

 olfactory pit, is a simple pigment spot or aboral ocellus. On the 

 oral surface is a well developed, pigmented, cupped ocellus of the 

 inverted type in which the cones are turned away from the light. 

 The canal which runs from the circular canal into the tentacu- 

 locyst, forms two blind canals at its base. 



Reproductive system. The sexes are separate and the 

 reproductive organs are simple, ductless gonads. When the 

 gonads are fully developed they appear as four colored rings 

 broken only by the narrow gonadial grooves. They are situated 

 in the gastric pouches and are endodermal in origin. The re- 

 productive cells are simply dehisced into the gastric pouches and 

 reach the stomach through the gonadial grooves. The fertilized 

 eggs are found later in the grooves of the mouth-arms and de- 

 velop in special pouches there. Here they reach the planula 

 stage and leave then the mother. 



Scyphostoma. The structure of the scyphostoma has 

 been often misinterpreted owing to the extreme contractility 

 of its muscle-bands which change the position of the mouth. 

 Thus it happened that investigators have described a manu- 

 brium and a gullet where such organs do not exist in reality. 

 The stem is quite short and thin. The tentacles are attached in a 

 circle around a flat peristome from the middle of which arises a 

 conical hypostome. At the extreme end of the hypostome is the 

 square mouth. The tentacles are solid and normally sixteen in 

 number, although as many as twenty-four have been observed. 

 The corners of the mouth mark the two perradial planes. In the 

 interradii of the peristome are four pits which are usually sup- 

 posed to be homologous with the subgenital pits of the adult 

 medusa. These pits are called septal funnels. They are formed 

 by the invagination of the ectoderm and lead into the wall of the 



