CHAP. III. NAUPLIUS-FORMS. 17 



mode of respiration. Whilst in all other Oniscoida the 

 abdominal feet serve for respiration, these in our cheli- 

 ferous Isopod (fig. 2) are solely motory organs, into 

 which no blood-corpuscle ever enters, and the chief 

 seat of respiration is, as in the ZoSse, in the lateral 

 parts of the carapace, which are abundantly traversed 

 by currents of blood, and beneath which a constant 

 stream of water passes, maintained, as in Zoese and 

 the adult Decapoda, by an appendage of the second 

 pair of maxillae, which is wanting in all other Edrioph- 

 thalma. 



For both these discoveries, it may be remarked in 

 passing, science is indebted less to a happy chance than 

 immediately to Darwin's theory. 



Species of Peneus live in the European seas, as well as 

 here, and their Nauplius-ltYOod. has no doubt repeatedly 

 passed unnoticed through the hands of the numerous 

 naturalists who have investigated those seas, as well as 

 through my own, 3 for it has nothing which could attract 

 particular attention amongst the multifarious and often 

 wonderful Nauplius-forms. When I, fancying from the 

 similarity of its movements that it was a young Peneus- 

 Zoea, had for the first time captured such a larva, and 

 on bringing it under the microscope found a Nauplius 

 differing toto eoelo from this Zoea, I might have thrown 

 it aside as being completely foreign to the develop- 

 mental series which I was tracing, if the idea of early 

 Naupliiform stages of the higher Crustacea, which in- 



3 Mecznikow has recently found Naupliiform shrimp-lame in the sea 

 near Naples. 



C 



