70 CONTRIBUTIONS TO AMERICAN HELMINTHOLOGY. 



The structure of the cirrus-coronet is difficult to ascertain on ac- 

 count of the semi-opacity of my mounted specimens. The pieces do 

 not seem to be more than eight in number; they converge anteriorly 

 where they are narrow and pointed; posteriorly they are wider, 

 with somewhat arrow-head shaped ends, which fit into the terminal 

 bulbous portion of the vas deferens. I have been imable to follow 

 the rest of this tube, or to find any trace of the testes. 



Sphyranura resembles P. oblongum and the precocious gill-cavity 

 stage of P. integerrimum, in possessing only one complete shell- 

 invested egg in the uterus at one time. This is very large (v. 

 supra) in relation to the size of the worm, being considerably larger 

 than the eggs of either P. integerrimum or P. oblongum. It con- 

 sequently forms a noticeable feature in the worms possessing it, and 

 is readily detectable with the naked eye. Numerous other eggs 

 may be seen in the oviduct formed of the ovarian ova with the in- 

 vesting foodyolk-balls, and by mvitual compression assuming various 

 forms. What I suppose to be the ovary is represented in the figure 

 to the right hand of the base of the muscular tube. I cannot find 

 any trace of shell-glaiid, transverse vitello-duot, or of a vagina. All 

 of these would undoubtedly be easily seen in fresh or well preserved 

 specimens. 



I regard the genera Gyrodaetylus, Dactylogyrus, Sphyranura and 

 Polystomum, as forming a very natural assemblage. All probably 

 live on the blood of their hosts, being found in positions where there 

 is a morc or less close superficial vascular plexus; all possess a caudal 

 disc armed with fourteen to sixteen small and two (rarely more) 

 large hooks, which enable the fish-parasites to secure themselves 

 firmly to the gill-filaments of their hosts. Those which possess 

 suckers formed around the smaller hooks are found attached to 

 smoother surfaces (mucous membrane of mouth and urinary bladder), 

 where the small hooks alone would have little purchase; even these 

 forms, however, pass through a suckerless stage in which they inhabit 

 the anterior respiratory part of the intestinal tract.^ The resem- 

 blance of the Polystomum-larva to Gyrodaetylus is very striking, so 

 that if any phylogenetic speculations niay be made from the obser- 

 vation of the ontogeny of an animal, the assumption is surely justi- 



so It must be remembered that the mucous membrane covering the hyoid arches of many 

 Chelonia has still a high respiratory signiflcaace. Vide Aga,ssiz: Caatrib. Nat^ Hiatt U. S- 

 Vol. l.j Ft. ii., pp. 271-^84. 



