MKl»rs.K OF woods HOLE REGION. 71 



The nervous system, or rather tissue, seems chiefly limited to the aboral pole 

 and concentrated about the sensory body (otocyst ?), whose function is probably 

 that of equilibrium. 



In form the Ctenophora are for the most part ovoid, pyriform, or spherical 

 organisms, of extreme delicacy of texture, making it almost impossible to lift a speci- 

 men from the water without its dissolving into a bit of formless slime. Cestus, or 

 Venae's girdle, is a rare exception to the. usual shape already indicated. In this form 

 (he body is greatly extended in the stomach plane and flattened in the funnel plane. 



t'tenophores are hermaphrodite, the gonads being borne on opposite sides of the 

 canals. Development is direct for the most part, in onl}' a few cases showing meta- 

 morphic phases. 



The Ctenophora are distinguishable into two fairly well-defined sections, namely, 

 those with tentacles and those without tentacles, or 



Tentaculata. — With more or less evident tentacles, at least during the earlier 

 larval history. 



Nontentaculata. — Devoid of tentacles during entire life history. 



TENTACULATA. 

 ORDER CYMPPID.E. 



Body more or less spherical or cylindrical, with two simple or pinnate tentacles which are retrac- 

 tile within lateral pockets. Aboral pole without wing-like processes. 



Family MERTENSIID^. 

 Body somewhat compressed iii the gastric plane, subtentacular ridges longer than the aubgastric. 



MERTENSIA Lesson (1843). 



Mertensia ovuin (Fabricius). 



Beroe ovum Fabricius. Fauna Groenlandica, 1780, p. 362. 



Cydippe ovum Eschscholtz, System der Acalephen, 1829, p. 25. 



Beroe jnTews Scoresby, Arctic Regions, 1820. 



Mt rti ttxiti xemrshi/i Lesson. Histoire Naturelle ties Zoophytes Aealephes, 1843. 



Merii Hi>i<i "rum \ Agassiz, North American Acalephee, L865, p 26 CI Die Ctenophoren der Plankton-Expedition, 



1898, p. 10. 



Body subspherical to pyriform, from 16 to 18 mm. in diameter. Acconling to A. Agassiz this 

 species is distinguished by a peculiar whirling motion in swimming, and by a distinct pinkish color; 

 bcily somewhat flattened. Only rarely taken at Woods Hole; commoner northward. 



Family PLEUROBRACHIID£. 



Body pyriform to spherical; subtentacular and subgastric ridges of about eejual length. 

 PLEUROBRACHIA Flemming (1822). 

 Pleurobrachia pileus (Fabricius). 



V,i mi pileus Fabricius, Fauna groenlandica, 1780, p. 361. Flemming, History British Animals. 1S28, p. 504. 

 Cydippe pileus Eschscholtz. System der Acalephen, 1829, p. 24. 



/'/' urdbrachia rhododactyhx L. Agassiz, Memoirs American Academy, Vol. IV, 1849, p. 314. 



Pleurobrachia pileus L. Agassiz, Contributions to Natural History of the United States, Vol. Ill, 1860, p. 203. Chun, Die 

 Ctenophoren Plankton-Expedition, 1898, p. 15. 



