ZOOLOGY 



SECT. 





Fro. r i 664. Balanoglossus. En- 

 tire : animal, br. branchial region ; 

 co. collar ; gen. genital ridges ; hep. 

 prominences formed by hepatic coeca ; 

 pr. proboscis. (After Spengel.) 



External Characters. Balano- 

 glossus (Fig. 664) is a soft-bodied, 

 cylindrical, worm-like animal, the sur- 

 face of which is uniformly ciliated. It 

 is divisible into three regions ; in front 

 there is a large club-shaped hollow 

 organ the proboscis (pr.) ; immedi- 

 ately behind the proboscis and en- 

 circling 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, bur- 

 rowing in sand or mud by means of 

 its proboscis. 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. 665, prob.) 

 has muscular walls ; its cavity opens 

 on the exterior usually by a single 

 minute aperture the proboscis pore 

 (prb. po.) rarely by two. Its narrow 

 posterior part or " neck " is strength- 

 ened by a layer of cartilage-like or 

 chondroid tissue, which supports the 

 blood-vessels. The collar is also mus- 

 cular, and contains one cavity or two 

 (right and left) separated from one 

 another by dorsal and ventral mesen- 

 teries, and completely cut off from the 

 proboscis cavity. The collar cavity 

 and also that of the proboscis are 

 crossed by numerous strands of con- 

 nective tissue of a spongy character. 

 The collar cavity communicates with 

 the exterior by a pair of cottar pores 

 ciliated tubes leading into the first 

 gill-slit or first gill-pouch. 



On the dorsal surface of the an- 

 terior part of the trunk is a double 

 row of small slits the gill-slits (Fig. 

 664, br.) each row situated in a longi- 

 tudinal furrow; these slits increase in 

 number throughout li!eT~ The~^most 

 anterior are in some species overlapped 

 by a posterior prolongation of the collar 

 called the operculum. A pair of longi- 



