632 PROFESSOR E, RAY LANKESTER; 
pterina with the Copepoda appears to me to have only the 
support of a certain resemblance of general form in its 
favour, such resemblance of general form being one which 
frequently recurs in the Arthropod series, and has the signi- 
ficance merely of a homoplastic agreement, @.e, is a like 
moulding of readily modifiable parts brought about quite 
independently in the cases compared by the operation of like 
adaptive causes. Other examples in relation to. the Eury- 
pterina have been previously cited by Professor Huxley 
(‘Lectures on Nat. Hist.,’ 1857), e.g. the Cumacea and the 
Zoea of some Decapods. I cannot find, on comparing a 
Copepod, on the one hand, with the full organisation, on 
the other, expressed by a combination of the characters of 
Limulus and the Eurypterina, any points which appear to 
me indicative of close affinity; the agreements are such as 
either are common to the majority of Arthropods or are 
agreements of general form, of a nature similar to those 
which exist between the macrurous Arachnida and the 
macrurous Decapod Crustacea. Such agreements as exact 
coincidence in the position of the genital apertures, in the 
number, form, and grouping of the appendages, in the dis- 
position of the eyes, in the development of sternal plates, 
and over and above the individual agreements such intimate 
connection as is implied by the multiplied significance of 
the combined occurrence of two, three, or more of these 
agreements, cannot be established as between the Copepoda 
and Limulus. 
Between Kurypterina and such Copepoda as Cyclops, there 
is a general resemblance of the form of body. We find a 
broad carapace covering segments bearing five pairs of 
limbs, followed by a tapering series of segments, of which 
the anterior carry limbs, and may be distinguished as a 
separate region from those which follow. But whilst the 
Copepod body terminates in a characteristic furcal postanal 
process, the Eurypterina present, like the Scorpion and 
King Crab, a single spine or plate. The number of seg- 
ments succeeding the carapace in the Copepoda is at most 
ten ; in the Eurypterina it is, as in the Scorpion, twelve. 
Most significant is the position of the genital apertures, 
which in Limulus (and presumably in the Eurypterina) is 
placed on the first segment succeeding the six-segmented 
carapace, whilst in the Copepods the whole series of five 
segments, bearing swimming feet (which would be compared 
to the lamelligerous feet of Limulus), intervene between the 
carapace and the genital segment. In structure and posi- 
tion the eyes on the carapace of Copepods have no resem- 
