40 CCELENTERATA. 



acquires a coelenteron, mouth, and tentacles. Longitudinal 

 ridges called tseniolse are formed in the coelenteron, septal 

 funnels are formed between the tentacles and mouth, and 

 from the septal funnels ectoderm cells are budded off that form 

 the four longitudinal septal muscles. This larva is called a 

 scyphistoma. 



The scyphistoma grows, acquires more tentacles, may bud 

 to form other scyphistoma, and usually acquires stolons, which 

 grow out from the body wall just above the base. From the 

 stolons new scyphistoma arise. Suhgenital pits make their ap- 

 pearance in the position formally occupied by the septal fun- 

 nels, and an ostium appears in each tseRiola near the oral surface. 

 In this way a ring sinus is formed. Gastric filaments are formed 

 on the edges of the tseniolse. 



From the oral side of the first eight tentacles sense organs 

 bud out. Eight lobes make their appearance opposite these 

 sense organs, each lobe divides into two lappets, between which 

 the sense organ lies. While these changes are taking place 

 constrictions running around the body appear and deepen so 

 the body is divided into a series of plates, each of which has 

 eight lobes, eight sense organs, and sixteen marginal lappets. 

 The disc at the free extremity is the oldest and most differen- 

 tiated. 



This stage is frequently called the strohila, but there is no 

 definite dividing line between scyphistoma and strobila. The 

 number of discs formed by a strobila seems to be dependent 

 upon conditions, probably largely food supply. 



Before the discs are ready to be detached as ephyrce the 

 tentacles disappear. Ephyrse are detached one at a time from 

 the free end as they mature. 



Up to this point students will be able to determine only part 

 of the points mentioned unless an abundance of material and 

 sections are provided. The remaining points are easily de- 

 termined. 



Examine a free ephyra. If it is alive, watch it swim. Find 

 the mouth, stomach, marginal lobes, marginal lappets, and 



