CHAPTER XXXIV 



OTHER UNSEGMENTED WORMS 



From the time of Linnaeus in 1758 until the end of the last century a 

 diverse group called Vermes, or worms, was recognized as one of the 

 primary groups of the animal kingdom. It has now been broken up into 

 several groups, some of which are considered phyla. Included among 

 these are Platyhelminthes, Nemathelminthes, Annelida, and the phyla 

 considered in this chapter. 



217. Phylum Nemertinea. — One of these phyla, by some classified 

 with Platyhelminthes, is Nemertinea (nem er tin' e a; G., nemertes, 



grroove 



A/foLf/-h 



Proboscis 



Ccrc/d^/a/ C/rrus 



B 



Fig. 90. — Cerehratulus, a nemertine. A, Cerebratvlus lacteus (Verrill), a common 

 species of the Atlantic Coast. The head seen from the ventral side. {From Pratt, " Manual 

 of the Common Iiivertebrate Animals," by permission.) Natural size. B, Cerehratulus sp. 

 from Naples, showing a side view of the head with proboscis everted. From a preserved 

 specimen. (From Sheldon, " Cambridge Natural History," by the courtesy of The Macmillan 

 Company.) X 2. 



unerring), which contains the bandworms. They are flat and bandhke 

 (Fig. 90), resembling somewhat in this respect the flatworms, but are 

 clearly distinguished by certain structural features, among which is the 

 presence of a long proboscis which lies in a sheath within the body, dorsal 

 to the ahmentary canal. This proboscis may be protruded anteriorly 

 and used as an organ of touch and also as a protective and defensive 

 organ. Another characteristic is the development of the hlood-vascular 

 system, which is seen here for the first time and which consists of a median 

 dorsal and two lateral trunks. These animals also possess an alimentary 

 canal with mouth and anus. They are generally considered as possessing 



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