116 



THE EARTHWORM 



tissue as to have a featherlike appearance in these transverse sections. 

 What functions do these muscle layers perform? (4) The innermost 

 layer of the body wall is the peritoneum which lines the body cavity; 

 it is a single layer of squamous epithelium. 



(d) The wall of the stomach-intestine is composed of three layers: 

 (1) The outermost is the chloragogue layer which is composed of 

 slender columnar epithelial cells containing numerous granules. This 

 layer is a highly modified visceral peritoneum and is apparently con- 

 cerned with the excretion of certain waste products. (2) Beneath the 

 chloragogue layer is a very narrow layer, the submucosa. It contains 

 some non-striated muscle cells, which are arranged so that some extend 

 in a circular and some in a longitudinal direction. In addition, fibrous 

 connective tissue surrounds numerous small blood vessels. What func- 

 tion do these vessels perform? (3) The innermost layer is the mucosa, 

 a layer of ciliated columnar epithelium. Are gland cells present? 

 How is the food mass moved along the length of the stomach-intestine? 



Sensory ceff\ 

 (rcocpt/or) ^^ 



epidermic 



mui>c/e coff 

 (c.ff&ctor) 



Fig. 57. — Sensory-neuro-muscular mechanism of the earthworm; arrows 

 indicate the direction of transmission of nervous impulses. 



(e) Examine the section as a whole again. What is the condition 

 of the layers of the stomach-intestine in the region of the typhlosole? 

 The contents of the coclom are likely to be confusing, because of the 

 irregular manner in which the septa and nephridia are cut. Under- 

 stand these parts and why they appear as they do in your section. 

 Locate the dorsal vessel, ventral vessel, subneural vessel, and lateral 

 neural vessels. Do you find branches of these blood vessels? Under- 

 stand the direction of blood flow. 



(f) Draw (X 1 projected size) a narrow rectangular strip from the 

 gut cavity through to the outside of the body, showing accurately the 



