COE : XEMEKTEANS OF WEST AND NORTHWEST COASTS. 7 



diverticula, a single pair of gonads develops between each pair 

 of these intestinal ai)pendages. A few species are viviparous. 



Deoelopment. — In the larval development, some forms (Lineidae) 

 pass through a complicated metamorphosis, with the formation of a 

 free-swimming larva of highly specialized form (pilidium, or Desor's 

 larva), but in other forms (Amphiporus, Cephalothrix) develop- 

 ment is direct, or is accompanied only by a shedding of the larval 

 integument. 



Habits. — Nearly all species are marine, living under stones, 

 among algae, or in burrows in the sea bottom or shore between 

 tides ; representatives of a single widely distributed genus (Stich- 

 ostemma) live in fresh-water pools, ponds, or rivers, and several 

 species live in moist earth in warm climates ; a few forms are com- 

 mensal, inhabiting the mantle chambers of lamellibranchs or of 

 ascidians, while the members of a single genus (Carcinonemertes) 

 are truly parasitic, living among the gill plates or egg masses of 

 various sj)ecies of crabs. 



Anatomical and Histological Structures, with Special 

 Reference to the Pacific Coast Species. 



The anatomical and histological peculiarities of the various organ 

 systems of the nemerteans as they were known previous to the 

 year 1895 have been presented by Biirger ('95; '97-: 03) in so 

 letailed and comprehensive a manner that it will be necessarj^ in 

 this article merely to call attention to those features which have 

 come to light from more recent studies, and especially to those 

 peculiarities in which the Pacific coast forms differ from those spe- 

 cies which have been previously described. 



These pecuHarities may best be presented in a brief sketch of the 

 different organ systems of the nemerteans, in which the deviating 

 (characters found in the Pacific coast forms, described on the follow- 

 ing pages, shall be included. The order of arrangement is the same 

 as that adopted by Biirger, in his Monograph of the Nemerteans of 

 the Gulf of Naples, which has been freely consulted in the prepara 

 tion of this chapter. To this monograph the reader is referred for 

 a comprehensive and detailed account of those anatomical peculiari- 

 ties of which it seems necessary to give here but a brief description, 

 extended only so far as to render intelligible the deviating characters 

 of the Pacific coast forms. 



