182 CHOBDATA. 



1. Compare the grouping of the individuals 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 two or three millimeters thick, and study it with 

 a low power of the microscope. Other pieces should be squeezed 

 in a finger-bowl 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 pipet. 



In the adult animal you may find: 



(a) Oral and atrial openings. 



(b) Pharynx, with the peri-pharyngeal bands and endostyle, 

 esophagus, the orange-brown corrugated stomach, and intestine. 



(c) The cerebral ganglia. 



(d) The long post-abdomen, with its hollow epicardium con- 

 nected with the pharynx. (The post-abdomen is really a stolon. 

 Recall Perophora.) If complete, the red-pigmented tip will be 

 seen. 



(e) The slowly pulsating U-shaped heart, situated very near 

 the tip of the post-abdomen. 



3. In the atrium, which serves as a brood-pouch, embryos 

 in all stages may be found. How do the eggs compare in size 

 with those of Molgula? 



4. Look for buds formed by segmentation of the post-abdo- 

 men (stolon). The "inner vesicle " of these buds, which gives 

 rise to the alimentary canal and atrial sacs, comes from the 

 endodermic epicardium, as in Perophora. Compare this with 

 Botryllus. 



5. If the material squeezed in the finger-bowl was quite fresh, 

 living embryos in all stages of development can be found, and 

 the tailed larvse will probably be found hatching during the first 

 hour or two. These swim rapidly, and usually swim away from 

 the light. Does this correspond with Botryllus? Is this nega- 

 tive phototrophism adaptive? 



