396 
POPULAR SCIENCE REVIEW. 
If we glance for a moment at the larval stage of that most 
specialised and highly developed of modern Crustacea the Crab, 
depicted on our plate (PL XC., fig. 11), we find that in its 
zooid state it has sessile eyes, a long body, destitute of any ap- 
pendages ; it has no walking legs, but it is a free-swimming 
form, performing its locomotion with its maxillipeds or jaw- 
feet, which are greatly developed, serving as a pair of long oars 
similar to those with which Stylonurus Logani is furnished. 
(PL XC., fig. 3). 
Indeed the larva of this highest form is the most apt illustra- 
tion of our ancient order the Merostomcita. 
Limulus is living to-day to represent his great ancestor in 
the Silurian epoch, but we find that the palaeozoic King-crabs 
are still more closely and successfully represented, not by the 
adult, but by the larval stages of the living King-crab, repre- 
sented in our illustration (compare figs. 6, 7, 8, and 9, on 
Plate XC., with figs. 21, 23, and 24 on Plate XCI. 
We thus arrive at another interesting deduction, namely, 
that the stages of development of the individuals of to-day 
are a reflection of the life-history of the class in past geological 
time. It is worthy of notice, when speaking of the Meros- 
tomata, to point out that we have intermediate forms affording 
characters between the long-bodied Pterygotus and the short- 
bodied Limulus , namely the genus Hemiaspis (see Plate XC., 
fig. 5). There are also three Russian forms named Pseudoniscus 
aculeatus , Exapinurus Schrenkii , and Bunodes lunula , in 
which the hinder segments of the body are sensibly diminished 
in size and reduced in number. 
A similar group of irregular forms (the Anomoura) exists 
among the living Decapoda. 
When we turn to the Phyllopoda and Ostracoda, among the 
Entomostraca, we find numerous forms in the palseozoic 
rocks, which are readily comparable with those now existing, and 
differing chiefly in their greater size as compared with living 
types. 
The one figured on our engraving (Plate XC., fig. 10), 
Dithyrocaris Scouleri , McCoy, will serve as an apt illustration 
of a palaeozoic phyllopod, reminding one strongly of the re- 
cent Apus and Nebalia. 
The Entomostraca were probably as abundant in past times, 
as at the present day, their remains often forming almost entire 
strata. 
We do not propose to treat of them in the present article, 
but merely to point out that they are the most persistent group 
among the Crustacea, being found from the Cambrian period 
to the seas of to-day ; lowness or simplicity in organisation, 
with great powers of vitality and reproduction superadded. 
