816 LAUVJL CESTOBE PA RA SI TES O F FISHES— L IXTOX. 



In No. 11 of the above list thirteen specimens of bluefisli were exam- 

 ined. In Xos. 18, 19, 20, and 1*3 there were forty-four fisli examined. 

 Cysts containing: larval Tetrarhyiichida' are rarely absent from the 

 blueflsh. 



The hooks as represented in figs. 9, 10 are quite different from those 

 heretofore i)ublished for this si)e{;ies. The specimen described in the 

 United States Fish Commission lleport for 1889 had the proboscides 

 retracted so that only a few hooks lying near the base of a proboscis 

 could be distinctly seen. The most distinctive feature of the i)robos- 

 cides of this species is the relatively long, slender, and nearly straight 

 hooks, which are tlie predominating kind, and in certain jiarts of the 

 proboscis the only kind. Most of the long slender hooks, when seen 

 under favorable conditions, M'ith proper enlargement, are seen to be 

 notched at the end, a feature which is characteristic of this worm. 

 This feature is easily overlooked, and I have repeatedly thought I had 

 found embryos which did not jiossess it, but upon a careful examination 

 of an everted proboscis, I have never failed to find hooks with their 

 extremities notched. 



I reproduce here, with some slight alteration, my account of this 

 worm given in an article published in the "American Naturalist.'" 



Another form of cyst I will notice briefly and illustrate by an embryo 

 taken from the surface of the liver of tlie cero [Scomberomorns rcgalis). 

 This cyst is long and slender, about 10.."j mm. in length and 1.5 in 

 diameter, yellowish, opaque, but broken in places so as to show the 

 outline of the blastocyst. 



The blastocj'st, which is set free when the walls of the cyst are rup- 

 tured, is long and slender, with a neck-like constriction at one end. 

 The head part thus set off is very changeable in form, expanding, con- 

 tracting, moving up and down and from side to side, and rotating 

 on the constricted neck. The longer part or body of the blastocyst 

 also undergoes much change of form by irregular contraction and 

 expansion, but these movements take i)lace more slowly than in the 

 head. The color is ivory white, slightly translucent when extended. 

 When compressed, the embryo is discovered lying in a coil in the head 

 of the blastocyst. The parenchyma of the head i)art is now seen to 

 be much coarser than that of the body i)art, the coarseness being due 

 to the presence of numbers of large, oval, retractile fluid spaces. The 

 l)arenchyma of the body is dense and finely granular, with smaller 

 retractile masses than those in the head i)art. When the head part of 

 the blastocyst is broken open, the embryo is released, but instead of 

 separating from the blastocyst, as in the case of an embryo Ehyncho- 

 hothriinii, the blastocyst remains attached to the scolex much like the 

 cystocercus of Twriia. The method of release, however, is <pute dif- 

 ferent from that of the cystocercus of most Tti^nia. Instead of unfold- 

 ing like the finger of a glove, the neck of the scolex first emerges in the 



February, 1887. 



