[41] ENTOZOA OF MARINE FISHES OF NEW ENGLAND. 493 



Length of hooks, 0.0G4 mm ; breadth of same at base, 0.02 mm . 



The proboscis, when fully extended, stands a little obliquely to the 

 axis of the body. In all the specimens that I have seen the proboscis 

 was either wholly extended or partly withdrawn bodily. In no case 

 was the proboscis inverted. These worms are able not only to with- 

 draw and to protrude the proboscis as a whole, but also to invert and 

 evert it. When the proboscis is retracted in mass the walls of the body 

 at the base of the proboscis are invaginated by the action of retractor 

 muscles, which are attached to the base of the sheath and iuserted on 

 the median parietes of the body. When thus retracted the proboscis 

 lies as a rigid cylindrical rod inclosed in a pouch made by the invagi- 

 nated anterior end of the body (Fig. 12). 



The protrusion of the proboscis seems to be effected by the propul- 

 sive force exerted by the fluid contents of the body cavity when forced 

 forward by muscular contraction of the body- wall. A retractor muscle, 

 or ligament, was traced from the interior of the proboscis sheath to the 

 apex of the proboscis. Inversion of the proboscis itself is effected by 

 this ligament, while eversion is produced by the action of the thick, 

 muscular walls of the sheath upon a granular fluid which it contains. 

 The hooks of the proboscis are arranged in quincunx order, thus giving 

 rise to rows parallel with the long axis of the proboscis, and also to 

 spiral rows. The body cavities of the females were crowded with myriads 

 of eggs. These were long-oval and each contained a fusiform embryo. 

 The outer covering of the ova is a delicate but rather thick, transpar- 

 ent membrane. Within this and immediately surrounding the embryo 

 is a thin but dense coat, which is much compressed at one end so as to 

 look like a loop, slightly compressed at the other. The embryo in 

 most of the ova had not developed sufficiently to indicate more than a 

 fusiform, granular mass lying within the dense hyaline inner coat of the 

 ovum. 



The spherical ovarian masses were in different stages of progress, 

 some having simple granular contents, others having secondary masses 

 within them, while in others oblong bodies, apparently young embryos 

 or the beginnings of ova, could be distinctly seen. 



Habitat. — Flat Fish (Pseudopleuronectes americarius), in intestine; 

 eight specimens. Wood's Holl, Mass., September, 1884. 



Echinorhynchus sagittifer, sp. nov. 

 [Plate VI, Figa. 1-2.] 



This worm was found in the peritoneum of several species of fish. 

 Although no adult specimens were fotiDd, the form of the immature 

 specimens is so different from that of any adult Acanthocephala with 

 which I am acquainted, and the structure and arrangement of the spines 

 are so remarkable, that I propose the name E. sagittifer for it. Of 

 course it is possible that it may subsequently be identified as the young 



