LIMULUS AN ARACHNID, 517 
are a series of marginal processes, the first corresponding to 
the first area, is a mere angular process of the integument, 
but the six which follow are in the form of movable spines.! 
Corresponding also to the six segments which bear the 
six spines (that is, to the six hinder segments of the seven 
in question) are a series of pits in the axial region of the 
tergum, a pair in each segment. 
—+ 
Fig 3. 
Fic. 3.—View of the abdominal carapace of Limulus polyphemus from 
below, the soft sternal region and appendages of the anterior six 
segments and the viscera having been removed. 
The figures vi1 to x11 upon the drawing (drawn from the object) are placed 
by the sides of the tergal entapophyses. The continuation of the same 
series (XIII to XVIII) is placed upon the chitinized sternal surface 
of the unsegmented region, which in Limulus represents the seventh 
abdominal and the five cylindrical preeanal segments of the Scorpion. 
These are deep invaginations of the integument forming 
hollow processes, pushed as it were into the body cavity and 
clothed internally with cartilage, the structure of which has 
been described by Gegenbaur (2); they give attachment to 
muscles and are well termed “ entapophyses”’ by Owen (7). 
When we look in the abdominal carapace of Limulus for 
representatives of the five cylindrical preanal segments of 
the Scorpion, we find nothing but a broad smooth area 
extending from the marking which indicates the hind 
? These spines I have seen slowly moving, independently of one another, 
in the living King Crab, indicating a separate musculature for each spine. 
