174 



AN INTRODUCTION TO ZOOLOGY 



This in its turn is followed by a strong muscular expansion, the 

 gizzard, occupying segments 17-19 or 20 ; but it may project 

 beyond this, carrying the septum with it. It has very strong walls 

 and a chitinous lining, in order to grind up the food before handing 

 it on to the intestine. 



The intestine itself is a long straight tube extending from 



lc 



fh. 



oe 



FIG. 55. Lumbricus herculeus. From Bourne. 



A, A view of the organs contained in the first twenty-two somites, as seen when the animal is 

 opened by a longitudinal dorsal incision, and the body walls are pinned out without cutting the 

 septa. The pins are placed in the srd, gth, and i8th somites. B, View of the first sixteen somites 

 of the same worm after removal of the alimentary tract, to show the nervous system and reproductive 

 organs. 



b.c., buccal cavity, cut across ; e.g., cerebral ganglia ; g., gizzard ; int., intestine ; nph., 

 nephrida ; od., oviduct ; oe., oesophagus ; ov., ovary in somite 13 ; ph., pharynx with radiating 

 muscular strands ; prv., proventiculus ; s., septa ; s.d., sperm duct ; s.f., seminal funnels ; spth. 

 spermatheccB in somites 9 and 10 ; sp.s., sperm sacs ; t., testis. 



segment 21 to the anus. In each somite it swells up into a saccu- 

 lation, which is well marked at the anterior end, but diminishes 

 as we pass backwards until it practically disappears at the posterior 

 end, and intersomitically the intestine is contricted where the septa 

 are inserted into it. The sacculations considerably increase the 

 area of the internal surface, an end also served by the dorsal wall 



