162 



TEXTBOOK OF ZOOLOGY 



in the form of a hollow tube turned back through the body inside 

 of a cavity called the proboscis sheath. By contracting the saclike 

 sheath, the proboscis may be everted and extended from the anterior 

 part of the body. 



The sexes are ordinarily separate and each individual possesses 

 gonads which are located laterally and between the intestinal 



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\\\ 



_ Rhynchodeum 

 ._ -Ocellus 



qanqlia 

 .-J^loric caecum 

 .^-Lateral mrve 



\ ffhynchocoe/ 



/nfccjfcinc 



Proboscis 



vSfcylefc 



_..Qonad 

 -MetractorM. 



Anus 



Fig. 78. 



Fig. 79. 



Fig. 78. — A nemertine worm, Lineus socialise with the body coiled. Natural 

 length about 15 cm. (Redrawn and modified from Hegner, College Zoology, 

 published by The Macmillan Company, after Coe.) 



Fig. 79. — Structure of the nemertine worm, Prostoma rubrum, as it appears 

 when flattened. (Redrawn and modified from Hegner, College Zoology, published 

 by The Macmillan Company, after Coe.) 



pouches. Both eggs and sperm are discharged from respective in- 

 dividuals through a dorsal pore and fertilization occurs in the sur- 

 rounding water. Following cleavage there is a helmet-shaped larva 

 called pilidium. Cilia develop on the lappets at the lower margins 

 of the body and on a patch at the opposite pole or apical plate. This 

 plate is the principal nerve center of the animal in this stage. The 



