218 



The genus MiCrOmSCUS, Fritz Miiller. 



(See PI. XCII). 



In the year 1870 Fritz Miiller examined a small Isopod found by him 

 parasitic on a Copepod (Calanoid) from Brazil, and described it under the name 

 of Microniscus fuscus as the type of a new genus of Bopyridse. Some years 

 afterwards I found a similar form off the Lofoten Islands clinging to a calanus 

 finmarchicus, and I recorded it briefly in my ,,0versigt" as a new species under 

 the name of Microniscus calani, though at the same time expressing my doubt as 

 to its being an adult animal somewhat in the following terms: ,,I feel, however, 

 great doubts as to the validity of the genus Microniscus, for both the form 

 described by Fritz Miiller and that examined by myself, exhibit so strong a re- 

 semblance to larval stages of other Epicarida, that I should be much inclined to 

 believe that both these forms represent immature animals, which would never 

 have reached to sexual maturity in the hosts on which they were found." On 

 re-examining the material of Microntsci subsequently collected, I am now in a 

 position to give full proof of the correctness of the above-quoted supposition. 

 The genus Microniscus, which is even regarded by MM. Giard and Bonnier as 

 the type of a distinct family, must indeed be altogether discarded, as only re- 

 presenting a transitory larval stage of Epicarida belonging to different families. 

 In the several forms of Epicarida only 2 larval stages have hitherto been de- 

 scribed, and these 2 stages are so very different both as to the general form of 

 the body and the structure of the several appendages, that it is rather difficult 

 to imagine how the one could develop from the other. Nor, so far as 

 I know, has the immediate transformation of the one stage into the other ever 

 been observed by any zoologist. Now the observations which I have had an 

 opportunity of instituting, and of which the results are elucidated by the figures 

 given on PI. 92, make it highly probable, that in all Epicarida there exists an 

 intermediate larval stage between the 2 formerly observed, and that this stage is 

 actually the Microniscus. Whether this stage in all cases is parasitic on Cope- 

 poda, I cannot say with certainty; but for 2 different forms at least, evidently 

 belonging to 2 different families, the parasitism on Copepoda is now proved. 



In one place on the west coast of Norway (Eggesb0nses), a Mimni'i*<-nx. 

 not apparently differing from the one first described as M. calani, was met 

 with not infrequently on the small Calanoid Pseud ocal anus elonyatus Boeck, and 

 it often happened that a single specimen af this Copepod carried 2 such para- 



