BOTRYLLUS, AMAROUCIUM 241 



(c) The cerebral ganglia. 



(d) The long postabdomen, with its hollow epicardium 

 connected with the pharynx. (The postabdomen 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 postabdomen. 



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- 

 abdomen (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 fingerbowl was quite 

 fresh, living embryos in all stages of development can be 

 found. Fresh specimens kept in a large jar of sea water dur- 

 ing the summer will discharge larvae. These swim rapidly, 

 and usually swim away from the light. Does this correspond 

 with Botryllus? Is this negative phototropism adaptive? 



The tailed larvae may be picked up with a pipette while 

 swimming, dropped into fixing fluid, and finally stained and 

 mounted. Others may be transferred to watch glasses and 

 studied. If the larvae are kept in watch glasses of sea water 

 for some hours some will attach. The dishes may be kept 

 in a cage under a wharf submerged in sea water, or in a dish 

 where pure sea water can be conducted to it. Under these 

 conditions they will develop readily, but they must be kept 

 clean from sediment by washing them with a gentle current 

 at least twice a day. 



In larvae that have been previously stained and mounted 

 observe : 



(a) The shape of the animal and its division into body 

 and tail. 



(b) The thick test, and the oral and atrial openings. 

 16 



