THE ANIMAL KINGDOM 



The proboscis is a hollow muscular organ with an opening, a pore, on the 

 left dorsal side of the neck. The mouth lies on the ventral side between 

 the proboscis and the collar. The collar, like the proboscis, contains a 

 division of the coelom, which opens to the exterior by a pair of pores 

 near the mid-dorsal line. Like the proboscis, the collar also is muscular, 

 and used by the organism as a means of burrowing in the sand where it 

 lives. 



PROBOSCIS COLLAR 



BALANOGLOSSUS. MOUTH gills 

 PiG_ 3_ — Balanoglossus, a typical genus of the sub-phylum Hemichorda. (Redrawn 



after Bateson.) 



The pharynx is divided into a dorsal portion which contains the numer- 

 ous gill-apertures and a ventral portion which functions as the digestive 

 passage of the pharynx. Posterior to the pharynx, the body contains a 

 series of gonadic sacs, each of which has a pore-like opening to the exterior. 

 The sexes are separate. 



In the so-called liver region, the intestine shows a series of paired 

 diverticula, each of which produces a corresponding bulging of the rela- 



LONG bUSCLE 

 OF PROBOSCIS 



BLOOD VESSEL 



Fig. 4. — Balanoglossus, the typical genus of the hemichordates, seen in left lateral 

 aspect. The possession of both dorsal and ventral nerve-cords links hemichordates 

 on the one hand with invertebrates and on the other with vertebrates. (Redrawn after 

 Stempell.) For the purposes of the diagram, the body of the animal is bent upon itself. 



tively thin body-wall. These diverticula are glandular and supposed 

 to have a digestive function, hence their name. Behind the liver-region, 

 the intestine passes without convolution directly to the posteriorly 

 situated anus. The circulatory system resembles that of annelids, but is 

 supplemented by a lacunar system of lymph spaces. 



The nervous system consists of dorsal and ventral nerve strands 

 containing occasional giant nerve cells. There are no special sense organs. 



