314 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



Parasitentragers, wo sie ihre Metamorphose bis zur definitiven Gestalt 

 des erwachsenen Tieres durchmachen" (p. 9) can hardly stand in 

 view of the fact that all copepod nauplii, as well those of parasitic 

 forms as of the free-swimmers, seek the surface of the water and 

 there swim about freely. 



Indeed, so far is Hofer's statement from being true that in the 

 Ergasilidae all the stages in the metamorphosis take place while the 

 larva is still a free-swimmer. No developmental stage of any mem- 

 ber of this family has ever yet been recorded as found upon any host. 



Later in the same year (1904) Gadd published an account of the 

 Parasitic Copepods of Finland, in which he gives another figure of 

 the nauplius of Ergasilus sieholdii, by far the best that has appeared. 

 He also gives the first detailed account of the appendages, but states 

 that he is not fully satisfied as to the number of segments they con- 

 tain. 



He notes the account given by Hofer and takes exception to the 

 same statements that have been discussed above. But he was com- 

 pelled to stop with the nauplius larva like Nordmann, though he 

 made repeated trials to carry the development farther with water at 

 difl^erent temperatures and diflerent degrees of salinity. As will be 

 seen, these accounts all describe the nauplius of E. sieholdii and that 

 species alone. The following description includes all the facts thus 

 presented and much additional material, based upon original observa- 

 tions made by the author upon two additional species of Ergasilus 

 (centrarcJiidarum and versicolor). 



Both of these are American species and the first of them was 

 carried successfully through two molts subsequent to the nauplius 

 stage, that is, up to the first copepodid stage. As all these accounts 

 agree in every particular where exact comparison is possible, the 

 development of the genus Ergasilus may be considered fairly es- 

 tablished. And this development must serve as the type of the 

 family, for at present nothing is known of that in any other genus. 

 But since Ergasilus has served also as the type for the ecology and 

 morphology, this only makes the account the more complete. 



Mating. — The males of the genus Ergasilus remained unknown 

 until 1863 when they were discovered and described by G. O. Sars 

 from specimens captured in the tow. This author rightly concluded 

 that the male leads a free and roving life in comparison with that of 

 the female, and based his conclusion upon the fact that the male 

 had never been observed before, and also upon the small size and 

 comparatively weak development of his second antennae. Sars then 

 adds in substance as follows: 



From this we are justified in assuming that the females are fertilized by the males 

 once for all during their early free-swimming development stages, and that this fertili- 

 zation is sufficient for the constant production of eggs and young during their subse- 

 quent fixed life. In fact it would be absurd to suppose that the males would be able 

 to hunt for the females while the latter were concealed on the fishes' gills. 



