AMAROUCTUM. 203 



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

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

 1924. 



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

 xxvi, 1924. 



AMAROUCIUM. (Sea-Potk.) 



Different species of this composite ascidian live at different 

 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 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 stornach, 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 



