Miscellaneous. 147 



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The Metamorphosis o/Penams. By \V. K. Brooks. 



Scarcely another fact in morphological science, standing alone, ex- 

 ceeds in interest the discovery that Penceus, a Decapod, passes through 

 a Nauplius stage. 



Those familiar with the literature of the subject will recollect that 

 Fritz Miiller kept under observation until it changed into a Protozoea 

 a Nauplius which he captured at the surface of the 



He also secured, in the ocean, a very complete series of larvae, 

 through which he identified his Protozoea with a young Macrouran 

 with the characteristics of the genus Penceus. 



He did not rear the Nauplius from a Penceus egg ; nor did he 

 actually observe the transformation into the young Penceus. Certain 

 over cautious naturalists have therefore refused to accept his conclu- 

 sions until more conclusive proof should be furnished. 



A number of stages in the development of Penceus have been 

 figured and described by Claus ; but as he also relied upon surface- 

 collecting, his evidence is open to the same objection. 



Although I have shown, by tracing from end to end the life-his- 

 tory of Lucifer, that this Macrouran undergoes a series of changes 

 almost perfectly parallel to those which Fritz Miiller describes in 

 Penceus, it is still desirable, as a matter of history, and in order to 

 set at rest those critics who refuse to give any weight to deductive 

 reasoning in morphology, to trace the life-history of Penceus, by 

 actually witnessing the changes. 



I have been able this summer, at the marine laboratory of the 

 Johns Hopkins University, to obtain the youngest Protozoea stage 

 of Penceus ; the stage which Fritz Miiller actually reared from the 

 Nauplius. I have had the good fortune to rear this larva in the 

 house, and to witness in isolated captive specimens every one of the 

 five moults between the first Protozoea and the young Peraeus. During 

 June and July, the breeding-season, the mature females cannot be 

 found inside the Sounds of our coast ; and as our boat is too small 

 for outside work during these windy months, I have not been able 

 to secure the eggs or Nauplii ; but this, the only gap in my series, 

 is filled by Fritz Miiller *s observation. The whole metamorphosis 

 of Penceus has therefoie been actually witnessed, and there is no 

 longer any room for criticism. 



Protozoeas apparently identical with the youngest one figured by 

 Miiller, and which a comparison with Lucifer shows to be in the 

 "first Protozoea " stage, were captured at the surface of the inlet 



by the hand-net. 



They were carefully drawn and measured, and were then placed 

 in tumblers, one in each tumbler, and were kept thus isolated and 

 under observation until they assumed the characteristics of the 

 Penceus, which they did after five moults. 



The first Protozoea has an ocellus, a very short rostrum, and traces 

 of the compound eyes, which are not yet movable. The first and 

 second antennae are Xauplius-like ; and the biramous second antennae 

 are the chief organs of locomotion. The labrum ha.- i short spine ; 



