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



Nephrops, Leach. 



The anatomical characters of Nephrops almost coincide with those of the genus 

 Homams, and but for the great dissimilarity of form of the first pair of pereiopoda, the 

 two genera would probably be classified as being only specifically separate. 



The branchial arrangement is identical, the structure of Nephrops approximating to 

 that of Homarus more nearly than to that of Nephropsis. 



Development. — The brephalos of the species of this genus has hitherto escaped 

 observation, but a short time since Professor Sars 1 captured what he considers to be the 

 "second larval" stage of Nephrops iwrvegicus, L., about 8 mm. long, and a second form 

 but little larger, 11 mm., that of a "young Nephrop>s," in its "first postlarval stage." 



Of the latter specimen there can be no hesitation in accepting Professor Sars's 

 diagnosis, and if the former should, by observation of the brephalos direct from the 

 ovum, demonstrate the correctness of this also, we shall find the apparently universal 

 plan of development in the Astacidea modified by a new arrangement in the middle of 

 the tribe. 



Assuming that Phyllosoma is only a peculiar form of Megalopa, the young of 

 Nephrops as shown by Sars is an intermediate form between the two. Thus we find 

 that a modified condition of the Megalopa stage characterises the brephalos of all the 

 families of the Trichobranchiata as far as is known, excepting the genus Spongicola, in 

 which it is hatched in the Zoea condition. 



The discovery of Professor Sars is undoubtedly one of considerable interest, as 

 hitherto the development of Nephrops has been unknown. I have long been making 

 efforts to get possession of specimens carrying ova in an advanced condition, but in a 

 large number that I have received from the Rev. Dr. Haughton and others, there was 

 not a female so laden. Nor were there any attached to those of Nephrops thomsoni. 



There are one or two points in Professor Sars's specimen that require notice. 



First, in general appearance it bears a resemblance to that form which we have con- 

 sidered to be a stage in the development of Aristeus, figures of which may be seen on 

 Pis. XLVI. and XLVII. of this Report, 



Secondly, it is noticeable for having the appendages of the cephalon and pereion in an 

 advanced stage of development. 



Thirdly, the several pairs of pleopoda are as yet only in the bud condition, and 

 the rhipidura does not exhibit any evidence of being present. 



Fourthly, the telson is formed on the type of that in the Brachyura rather than on 

 that of the Macrura. 



It is remarkable that animals so nearly allied as Nephrops and Homarus should exhibit 



1 Archivf. Mathem. og Naturvidensh., p. 159, pi. i., Christiania, 1884. 



