CHORDATA. 



309 



On the other hand there is a connective around the oesophagus 

 and a ventral nervous cord as in Annulata, and it shows no 

 signs of segmentation (see Fig. 151). 



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 



FIG. m 



FIG. 151. Balanoglossus (Male). After Bateson. 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 determine what features of Balanoglossus tend to ally it with the 

 chordates. What are the habits of the animal? Where do the earlier 

 zoologists class Balanoglossus? 



state, particularly, that their relation to the chordata is sug- 

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

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

 forms are usually attached, many of the larval organs be- 

 coming much changed or even wholly lost in consequence of 

 the changed mode of life. The adults have been variously clas- 

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

 by budding and form colonies from the fact that the buds 

 remain associated. 



3. Amphioxus (lancelet) possesses the characters 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 



