38 CCELENTERATA. 



(6) Two depressions, one above and the other below the 

 tentaculocyst. These have been assigned olfactory functions, 

 and are called the olfactory pits. Evidence of function is lack- 

 ing. 



Make a drawing showing the profile of the entire animal, and 

 show the structure of at least one quadrant, as seen from the oral 

 surface. 



8. If time permits, study developmental stages. 



The eggs are shed through the mouth and frequently be- 

 come entangled in the oral arms, where they may develop into 

 planulse. Most of the eggs are set free in the water, where they 

 develop. 



The planula after swimming some time attaches by one end, 

 acquires a ccelenteron, mouth, and tentacles. Longitudinal 

 ridges called ta3niola3 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. Subgenital pits make their ap- 

 pearance in the position formally occupied by the septal fun- 

 nels, and an ostium appears in each ta3Riola near the oral surface. 

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

 on the edges of the tseniolae. 



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. 



