CHORD ATA 313 



the nervous system is dorsal; and gill-slits occur. On the other 

 hand there is a connective around the esophagus and a ventral 

 nervous thickened band as in Annelida, and it shows little or 

 no signs of segmentation (see Fig. 153). 



2. Tunicates (sea-squirts, ascidians, etc.) comprising a 

 variety of forms which may be said, on the whole, to be de- 

 generate in the adult condition. It is in the larval or tadpole 

 state particularly that their relation to the Chordata is sug- 

 gested. In the larva they possess a notochord especially in the 



Fig. 153. 



Fig. 153. Balanogtossus (Male). After Bat^son. a, anus; m, mouth; p, proboscis; po,, pores, 

 the openings of the gill-slits; ts., testes. 



Questions on the figure. — Make reference to other texts and figures and de- 

 termine what features of Balanogtossus tend to ally it with the chordates. What 

 are the habits of the animal? Where do the earlier zoologists class Balanogtossus? 



tail region, a dorsal nervous system, and gill-slits. The adult 

 forms are usually attached, many of the larval organs becoming 

 much changed or even wholly lost in consequence of the 

 changed mode of life. The adults have been variously classified 

 as worms, mollusks, etc. Many of the tunicates multiply by 

 budding and form colonies from the fact that the buds remain 

 associated. 



3. Branchiostoma {Amphioxus; lancelet) possesses the char- 

 acters above mentioned as belonging to all the Chordata, except 

 that there is no true heart. In addition it has a fish-like body, 

 and the muscles are arranged in segments which appear exter- 



