240 CHORDATA 



from the parietal wall of the atrial cavity.) The inner vesicle 

 may be seen partly constricted into three divisions — the 

 pharynx and the two atrial sacs. From which "germ layer" 

 then are these parts in the bud derived? 



5. Look for the tailed larvae or "tadpoles" near the sur- 

 face and on the side turned toward the light, in a dish in 

 which Botryllus has been kept for an hour or two. Is this 

 positive phototropism advantageous? Examine a larva under 

 a microscope. 



Drawings of the adult, the young colony, and the larva 



are desirable. 



Grave and Woodbridge: Botryllus schlosseri, Pallas: The Behavior and 

 Morphology of the Free-swimming Larva. Jour. Morph., 39, p. 207, 



1924. 

 Herdman, E. C: Botryllus. Liverpool Marine Biol. Com. Memoirs, 



xxvi, 1924. 



AMAROUCIUM (Sea Pork) 



Different species of this composite ascidian live at differ- 

 ent depths and show minor structural differences, especially 

 in the tests. Colonies may be found abundantly on piles and 

 they are frequently brought up with a dredge. 



1. Compare the grouping of the individual in the colony 

 with Botryllus. Is there any regularity in the number of a 

 group connected with a common cloacal cavity? 



2 With a sharp knife, cut a section vertical to the surface 

 of the mass, and 2 or 3 mm. thick, and study it with a low 

 power of the microscope. Other pieces should be squeezed 

 in a fingerbowl half full of sea water, the expressed material 

 (adult animals, fragments, embryos, etc.) allowed to settle, 

 and then rinsed with clean sea water. A few entire adults 

 may be picked out with a pipette. 



In the adult animal you may find: 



(a) Oral and atrial openings. 



(b) Pharynx, with the peripharyngeal bands and en- 

 dostyle, esophagus, the orange-brown corrugated stomach, 

 and intestine. 



