218 THE VOYAGE OF H.M.S. CHALLENGER. 



numerous observers has ever taken any specimen of the genus with ova, or procured the 

 young animal immediately from the parent, or obtained a Nauplius, so as to establish the 

 identity of the relationship, as has been accomplished with nearly every other group of 

 Crustacea. 



Not only is this the case, but among the large number of specimens that have passed 

 through my hands in connection with the Challenger collection, and among all those 

 preserved in the National Museums in London and Paris, not one specimen that I have 

 seen carried a single ovum or even showed a trace of their attachment, yet such traces 

 are very commonly found in the various genera in the Trichobranchiata and Phyllo- 

 branchiata of the same order. 



This circumstance has led me to infer that the ova of Penseus and its allies are 

 not attached to the parent or carried about as in the Phyllobranchiata, but deposited in the 

 open waters soon after they are extruded, although Risso says 1 that Aristeus (Penseus) 

 antennatus and Penseus mars carry their ova in July, and that those of the latter species 

 are of an orange colour, " roux aurore." 



This idea appears to receive support from the recent researches of Professor Brooks on 

 the genus Lucifer, in which he shows that the ova are not attached to the parent by any 

 viscous membrane, but appear to be entangled amongst the pereiopoda, where they 

 remain for a day or two only, and are then hatched in the Nauplius form. 



The difficulty of artificially preserving these delicate young forms in life has not yet 

 been overcome. Those, of the commonest species, and consequently we may assume the 

 hardiest in character, have not been preserved alive beyond the second stage. It is there- 

 fore the more desirable that we should be able to determine a very close resemblance of 

 form in order to enable us to accept the observation as conclusive. 



Professor Brooks has taken the embryo from the ovum procured from Lucifer, and 

 found it to be in a Nauplius condition. This fact having been established, there is no 

 reason why the brejmalos of Penseus, which has never been demonstrated, and which we 

 assume to be incubated in the surface waters of the ocean, may not also be hatched in 

 the form of a Nauplius. But Dr. v. Willemoes Suhm's observation tends to the opinion 

 that the brephalos of Sergestes is hatched as Xylaphocaris in an eyeless condition. 



These several points, namely, the variation in the nervous system, the difference in 

 the structure of the branchiae, the manner in which the ova are deposited, the way 

 in which they are probably impregnated, together with the early condition of the 

 brephalos, demonstrate clearly a broad demarcation from those families in which the gills 

 are either trichobranchiate or phyllobranchiate. Like them they may be separated into 

 two groups, the Normalia and the Aberrantia. The former contains the families Pena?ida3 

 and Sergestidse, the latter, the Eucopidae, and such Schizopoda as have the branchise 

 arborescent, and hatch the brephalos in a Nauplius stage, as shown in the annexed table. 



1 Hist. Nat. des Crust, des Environs de Nice, pp. 96, 97. 



