194 CHORDATA. 



Certain organs are distinguishable through the tough tunic 

 which incloses the body. The endostyle, a ciliated groove look- 

 ing like a white thread along the mid-ventral line of the pharynx 

 or branchial basket, will serve as a guide in orienting the animal. 

 Determine dorsal, ventral, anterior, right, and left aspects. 



Make a drawing of an expanded animal. 



4. The tunic or test can be removed by cutting through it 

 with scissors, taking care not to injure the mantle or body-wall. 

 Enlarge the opening made in the tunic and strip it from the body. 

 Where is the tunic most firmly attached? Examine a small 

 piece of the tunic microscopically. Are blood-vessels visible 

 in it? Does it contain any cells? 



5. For further study use both fresh and preserved material 

 from which the tunic has been removed. Identify as many 

 organs as possible through the mantle. In a living specimen 

 note the beating of the heart (the heart is on the right side) and 

 the frequent reversal of the direction of the pulsations. The 

 endostyle, longitudinal pharyngeal folds, intestine, gonads, gono- 

 ducts, renal organ, and subneural gland are also visible through 

 the mantle. 



6. Note the muscle bands of the mantle which serve to con- 

 tract the body and especially the siphons. Where are the mus- 

 cles best developed? Is there any definite arrangement of the 

 muscle-bands ? 



7. Fix a large specimen by pins through the siphons, and 

 with scissors and fine forceps remove a large section of the man- 

 tle from the left side, between the digestive tract and the siphons, 

 injuring the underlying pharynx as little as possible. The large 

 space between the pharynx and the mantle, laterally and dor- 

 sally, is the atrium, or peribranchial chamber, which is formed 

 as an ectodermal involution. Into this atrial cavity open the 

 intestine and the gonoducts, and also the numerous stigmata of 

 the pharynx. Ventrally the pharynx is fused with the mantle 

 in the region of the endostyle. 



1. On each side of the upper part of the pharynx six longi- 

 tudinal pharyngeal folds will be seen. 



