1905.] NATURAL SCIENCES OF PHILADELPHIA. 397 



XI, are divided into from 10 to 20 slender, pyriform lobes which fill a 

 large part of the somite. Sperm sacs are either altogether absent or 

 very small. The sperm funnels occupy a great part of XI, are slender, 

 about 6 to 8 times as long as thick, nearly cylindrical, more or less 

 folded when m situ, and slightly contracted near the mouth, the margins 

 of which are provided with a ciliated roll or lip. The A^as deferens is 

 about three times as long as the funnel, closely but very variously 

 folded in XII, and has the terminal part somewhat enlarged and cili- 

 ated. It opens into the small, depressed, spheroidal, glandular and 

 opaque atrium, which itself opens on the medial side of a small bursa 

 in the position of the ventral setae. The bursa can be everted as a 

 conical penis (fig. 27). 



Somewhat like the testes, the ovaries are subdivided into about 20 

 ellipsoidal bodies, each with a cross division, on one side of which is one 

 or several large ova, and on the other a number of small ones. A small 

 ovisac pushes back from septum ^^^^, but is never extensively devel- 

 oped. The spermathecae (fig. 28) are small, pinkish, pyriform tubes 

 without diverticula or distinct ducts, which communicate with the 

 lumen of the oesophagus in V and with the exterior in the furrow ^, 

 near which they bear a circle of glands chiefly aggregated into an an- 

 terior and a posterior group. 



This is an exceedingly pretty and active little worm which crawls 

 rapidly and clings closely to surfaces. It is extremely abundant among 

 the eel grass thrown on shore near high-water mark, and which accumu- 

 lates in great quantities in sheltered coves. Its special habitat is a 

 certain stratum in the bedded masses where the plant is neither soaked 

 in water and much decayed, nor dried by the sun and air as in the up- 

 permost layer, but where it remains moist and coated with- a layer of 

 diatoms on which the worm feeds. If sexually active worms be re- 

 moved from such conditions and placed in clean salt water without 

 diatoms the genital organs quickly shrink, but if kept in even a small 

 quantity of moist eel grass exposed to moderate light they continue 

 to reproduce. These worms are much parasitized by a monocystid 

 gregarine. The species is known from Casco Bay, Maine, to Mne>yard 

 Sound, Massachusetts. 



Bibliography. 



Beddard, F. E. On Certain Points in the Structure of CUtcUio. Proc. Zool 



Soc. London, 1888, 485-495, PI. XXIII. 

 Bourne, A. G. Notes on the Naidiform Ohgochseta. Quar. Jour. Mlcr. Sci 



XXXII (1891), pp. 349-356, Pis. XXVI and XXVII. 

 Claparede, E. Etudes Anatomiques sur les Annehdes, etc. Mem. Soc. Phys 



Geneve, XVI (1861), pp. 101-110, Pis. Ill and IV. 



