260 PROCEEDINGS OF THE AMERICAN ACADEMY 



XVIII. 



PRELIMINARY COMMUNICATION ON THE HOST OF 

 NECTONEMA AGILE, Verk. 



By Henry B. Ward. 



Presented by E. L. Mark, November 9, 1892. 



In a paper on Nectonema agile, published last June,* I endeav- 

 ored to show, from purely morphological evidence, that, although 

 known only as a free-swimming adult, this worm must he parasitic 

 in early life. I suggested further some small fish or crustacean 

 (Paliemonetes) as its probable host. Last October Prof. J. P. 

 McMurrich t very kindly sent me a nematode with the following 

 description: "I obtained last summer from a Palaemonetes this 

 nematode lying curled up in the thoracic cavity. In general form 

 it suggests Nectonema, but lacks the lateral bands of setae so 

 characteristic of the free-swimming form; the parasitic habit may 

 account for that." 



The alcoholic specimen, which was in two pieces when received, 

 measured 75 mm. in length, and 0.5 mm. in diameter, being thus 

 longer than auy adult female Nectonema hitherto reported, and 

 surpassing even the avarage male (68 mm.) in length, so that if 

 this parasitic worm is Nectonema, the difference in size between 

 the sexes appears less evident than was stated in the paper cited. 

 Externally this parasite exactly resembles the adult female Nec- 

 tonema in all respects except in the entire absence of the rows of 

 hairs which are found on the cuticula of the median lines of the 

 latter. Cross sections show conclusively that it is a female Necto- 

 nema in approximately the same stage of development as that rep- 

 resented in Figure 58 (Plate IV.) of the paper already referred to. 

 The thin body wall encloses a crowded mass of nearly developed 

 eggs, which indicate that this specimen is quite as mature as those 

 captured free swimming. The cuticula is clearly divided into 



* Bull. Mus. Comp. Zoiil, Vol. XXIII. No. 3. 



t I desire to return my sincere thanks to Prof. McMurrich for his kindness 

 in sending me this specimen. 



