298 PROCEEDINGS OF THE NATIONAL MUSEUM VOL. 108 



the posterior one. Testes separate, vas deferens short and recurved. 

 Larvae hatch in the cypris stage. 



Description: The parasites are attached to the ventral surface of 

 the host's abdomen; in the case of the syntypes, on segments 3-6. 

 The snytype specimens have a length of approximately 5 mm., while 

 the additional examples from the same locality measure 6 mm. Those 

 from the Albatross collection are only 2 mm. long and are very im- 

 mature. The specimens from any one host individual are all fairly 

 uniform in size. 



The curious shape of the sacs can best be explained by reference 

 to the figures. In general, the parasites have the appearance of 

 a 2-pronged fork, with the posterior arm equal to or usually 

 a little longer than the anterior one. Each arm is rather 

 slender at its point of origin and becomes broader toward the tip. In 

 the mature specimens the lesser diameter is 0.5 to 0.75 mm. and the 

 greater diameter about 1 mm. The anterior arm terminates in a 

 nipple-like prominence, covered by a bulbous sheath which is a 

 continuation of the external cuticle. The stalk of the mature speci- 

 mens is marked by three circular grooves. 



The external surface is covered by a thin cuticle which has the 

 appearance of being finely striated. This, however, is due to the 

 innumerable muscle fibers, chiefly cu-cular, that lie beneath it. 



The rather narrow mesentery proceeds from the stalk towards the 

 concave surface of the sac where it passes into both arms and continues 

 to theu- extremities. At the anterior end its termination is somewhat 

 acute but at the posterior end it flares out to form a thin plate. 



In the immature animals from the Albatross collection one can see a 

 compact ovarian mass running the entire length of the animal and 

 filling up the cavity of the sac. In the other specimens the visceral 

 mass is collapsed and completely empty but the mantle cavity is 

 filled with larvae in the cypris stage. This feature is rather uncom- 

 mon, since the great majority of Rhizocephala hatch in the nauplius 

 stage of development. 



Although the colleteric glands could not be found with certainty 

 in the large animals because of the degenerated condition of the visceral 

 mass, they were evident in the immature specimens. They occur 

 alongside the stalk at the base of the anterior arm and are of very 

 simple construction, consisting of several layers of epithelium sur- 

 rounding a single unbranched canal. 



The testes are two small elongated pouches situated near the tip 

 of the posterior arm with their blind ends directed towards the stalk. 

 The outer wall of the organ is made up of a well-defined structureless 

 membrane. Each gives rise to a short vas deferens that soon reverses 



