THOMPSON: METAMORPHOSES OF HERMIT CRAB. 175 
The foregoing description for the second segment will apply 
equally well to segments one arid three except that in the former 
the anterior attachments are on the cephalothoracic walls. The 
fourth segment has a weak loop muscle which barely reaches the 
end of the loop muscle from segment three. Posteriorly its descend¬ 
ing portion seems to be attached at the articulation between seg¬ 
ments five and six. The fifth segment has only pleopodal, trans¬ 
versalis, and ventralis muscles. The sixth segment has pleopodal, 
transversalis, and ventralis, and the last mentioned muscle lies 
beneath the nerve cord. 
The muscles of the zoeae are on the whole similar to those of the 
glaucothoe, but less well developed and with weak attachments. 
The pleopodal muscles are wanting, except those for the uropods 
which come in with the fourth zoea. The three earlier zoeae have 
also the fourth segment like the fifth from the absence of loop- 
enveloping muscles. 
Mature glaucothoe, adolescent crabs, and adults have a musculature 
of a totally different type. The extensors are extremely weak; a 
thin layer of fibers — the integumentary muscles — lines the integu¬ 
ment beneath the nerve cord ; the flexors are bulky and those of the 
right side are considerably larger than those on the left. But the 
flexors on both sides are merely a series of strongly diagonal bands 
with the more dorsal fibers running almost transversely. Minor 
peculiarities present themselves in the different segments, but there 
is nothing which suggests either transversalis or loop-enveloping 
muscles, although descending, lateralis, and ventralis muscles are 
doubtfully identifiable. These muscles have been compared to the 
chevron-like muscles of Gebia and Callianassa and described as a 
crowded series of such “chevrons” (Bordage, ’ 93 ). 
If these muscles are to be identified with their forerunners in the 
larvae, a study of their metamorphosis becomes imperative. But 
unfortunately this could not be attained in as complete a form as 
might be desired. The changes are crowded into a comparatively 
short period near the end of the glaucothoe phase, the degenerative 
processes make it difficult to secure good preservation and there 
seems to be a slight reconstruction or remodeling near the very end 
of the alterations. The following data are at hand, however, from 
several individuals, and from them a general notion of the homol¬ 
ogies of the adult muscles can be obtained. 
