i nm ag eal 
AES UE PE En eee eee Oe 
J. D. Dana on Cephalization. 7 
organs) of a Crab. But in Limulus there is extreme of degra- 
dation, all the members being large and stout feet, only the basal 
joints of the feet serving as Jaws,—the body being enormously 
enlarged by mere vegetative growth,—the antenne wanting, or 
reduced to a pair of aor and the animal sluggish, a sport of 
the waves on a beac ile in Insects, there is extrem 
cephalization, the pairs of feet only three and pi pat small and 
slender, and the body minute in comparison—the antenne well 
develo ped and serving as delicate organs of sense—the animal 
active, and wonderful in its instinctive habits and knowledge. 
The parallelism, above shown, between Insecteans and 
under the classes of Insecteans and Crustaceans constitute par- 
allel series, the first two of each being closed types, within the 
range 0: of normal variation, and the last one of eac 
and Hntomostracans) being a degradational type, though differ- 
ore one from the other, in kind of degradation. The parallel- 
ism between the series would be well exhibited if the orders 
were thus named : 
tween Deca ntomostracans: on the ree hey lie 
quite out of the range of either. The Decapods, in their de- 
dational species, pass almost into Entomostracan fora: and 
tae into Tetrad s. So among Insec i 
e the same isolated position and canned limits. Insects, in 
E their degradation, sppEnaes to Myriapods, not to Spiders. 
| ers 
more ney eee Insects and Crusta- 
There is, here, a cross affinity aa Insecteans and Crus- 
taceans which is of great interest. The relation of common Spi- 
ders to Fraebpuea bas a Sree is seen, aes in me a 
* The 
mouth-organs and naa gent of fest; of a ds, in gee throug 
i ite number of segments and feet. Hence, to include 
iene 
A tera, as done by. some naturalists » who ado opt the oat ai vision of in 
Profes siz recognizes the same three classes of Articulates, as above, by 
the writer, and the same subdivisions, or Fane rs, of Insecteans, but “ from embryo- 
logical data.” The writer t felt y to deprive Spi dere and Myrinpods of 
nosects, C: rustaceans and 
