GENERAL STUDY OF TYPICAL CHORD ATES 13 



and the stomach (Ciona, Corella, Ascidia) in which case it is commonly single, or 

 may be attached to the inside of the mantle (Cynthia, Molgula), in which case 

 a pair of such glands is often present. From the ovarian part arises an oviduct 

 and from the testicular part a vas deferens. The two ducts run in close contact 

 with each other (and in some cases fuse to one duct) and open into the atrial 

 cavity near the atrial siphon. In Ciona the two genital ducts are found closely 

 attached to that side of the intestine which faces the pharynx, and in this posi- 

 tion run far forward, opening into the atrium some distance above the anal open- 

 ing. The genital opening in Ciona is colored red, due to the presence in its walls 

 of red vesicles, supposed to have an excretory function. In Molgula and other 

 members of the family Molgulidae there is a large saclike organ on the right side, 

 believed to be excretory in nature, but the presence of excretory organs in the 

 tunicates is more or less uncertain. 



In the dorsal part of the mantle, between the two siphons, will be found an 

 elongated mass, the ganglion, which constitutes the entire central nervous system 

 of the adult tunicate. Nerves may be seen extending from its ends to the siphons. 



Draw the dissection. 



3. The structure of the pharynx. Make a longitudinal slit in the side of 

 the pharynx forward through the oral siphon and spread out its walls. In the 

 median ventral line of the pharynx there is present a conspicuous white cord 

 extending the length of the pharynx. This is the endostyle or hypobranchial 

 groove, whose walls are composed of glandular and ciliated cells, the former 

 producing mucus. Directly opposite the endostyle in what may be designated 

 the median dorsal line of the pharynx is located the dorsal lamina. This in 

 some tunicates (Ascidia, Cynthia, Molgula) consists of a delicate membranous 

 fold of the pharyngeal wall, while in others (Ciona, Corella) it consists of a row 

 of processes called languets and resembles a fringe. At the anterior end of the 

 pharynx at the bottom of the oral siphon there generally occurs a circlet of 

 tentacles or irregular processes of the wall, and posterior to this is a grooved 

 ridge, the peri pharyngeal band, in which the anterior ends of endostyle and 

 dorsal lamina terminate. The lateral walls of the pharynx in some tunicates 

 (Molgula, Cynthia) exhibit a definite number of longitudinal folds. 



Cut out a small piece of the pharyngeal wall, mount in water, spread out 

 flat, and examine under the low power of the microscope, or examine prepared 

 slides. The wall is found divided into squares by means of longitudinal and 

 cross bars. Within each square so formed are seen several of the elongated 

 gill slits or visceral clefts, separated from each other by smaller bars. The 

 gill slits are commonly parallel to the longitudinal bars but may be curved 

 (Molgula). On the longitudinal bars there are often present finger- like processes 

 or papillae which have been shown to aid in pushing the food-containing mucous 

 strands toward the esophagus. Draw a portion of the pharyngeal wall. 



For further details of the anatomy of tunicates consult P and H, pages 14-21 ; 

 CNH, Vol. VII, pages 35-62; N, pages 50-52, H > P a 8 es 55~6- 



