xm 



PHYLUM CHORDATA 



diate allies ; the other, the Ptero- 

 branchia, including Cephalodiscus 

 and Rhabdopleura. 



External Characters and 

 Ccelome of Enteropneusta. 

 Balanoglossus (Fig. 714) is a soft- 

 bodied, cylindrical, worm-like animal, 

 the surface of which is uniformly 

 ciliated. The size varies extremely in 

 the different species, some being quite 

 small 2 or 3 centimetres, while other 

 species are of comparatively large size 

 and may be as much as 2J metres in 

 length. .It is divisible into three 

 regions ; in front there is a large 

 club-shaped hollow organ the pro- 

 boscis (pr.) ; immediately behind the 

 proboscis and encircling its base is a 

 prominent fold the collar (co.) ; the 

 third region or trunk is long and 

 nearly cylindrical, but somewhat 

 depressed. 



Balanoglossus lives in the sea, 

 usually in shallow water, burrowing 

 in sand or mud by means of its pro- 

 boscis : one species has been found 

 swarming on the surface of the sea. 

 Numerous glands in the integument 

 secrete a viscid matter to which 

 grains of sand adhere in such a way 

 as to form a fragile temporary tube. 

 The proboscis (Fig. 715, prob.) has 

 muscular walls ; its cavity (pro- 

 boscis-ccelome) opens on the exterior 

 usually by a single minute aperture 

 the proboscis-pore (prb. po.) rarely 

 by two. In some species the pro- 

 boscis-pore does not communicate 

 with the proboscis- ccelome, but ter- 

 minates blindly, and may send off a 

 narrow tubular diverticulum which 

 opens into the neuroccele. The nar- 

 row posterior part or " neck " of the 

 proboscis is strengthened by a layer 



of cartilage-like or chondroid tissue, FIG 7U .-Baianogiossus. 

 which supports the blood-vessels. The 

 collar is also muscular, and contains one 

 cavity, or two (right and left) cavities 



En- 



tire animal, br. branchial region ; 

 co. collar ; gen. genital ridges : hep. 

 prominences formed by hepatic 



P roboscis - < After 



B 2 



