THOMPSON: METAMORPHOSES OF HERMIT CRAB. 149 
before a shell was entered and considered that the desire for a shell 
arose from the anatomical changes. The extreme brevity of his 
record, however, lias been a cause of much confusion. It was not 
clearly shown whether this metamorphosis without a shell was the 
typical developmental sequence or only a frequent happening. 
Moreover, the amount of the asymmetry attained at this time was 
not certainly defined. Hence the record has been interpreted to 
mean that the change from the glaucothoe to the adult form was 
gradual and covered several ecdyses (Bouvier, ’91). But I am 
convinced that Agassiz intended to indicate the change as occurring 
with a single ecdysis and the figures published by Faxon (’82) sup¬ 
port this contention. These show four zoeae, and in less detail a 
fifth stage which is identified with the genera Glaucothoe and 
Prophvlax. Immediately following the fifth stage comes a stage 
entitled “age when it takes up its abode in a molluscan shell,” and 
this figure depicts a crab with almost adult asymmetry, but bearing 
minute rudiments of pleopods on the right side of the abdomen. 
The main outlines of Pagurid ontogeny had now become clear. 
The young passed through several zoea stages and then moulted to 
a glaucothoe phase analogous to the megalops of the true crabs, and 
as with them the mysis phase was suppressed (Claus, ’76) into the 
last of the zoea stages, the metazoea (Claus, ’85). The anatomy of 
the glaucothoe, however, remained almost unknown and the details 
of the metamorphosis to the adult form obscure. For as already 
noted, considerable uncertainty existed as to whether the larva 
passed to the adolescent phase directly or gradually. Since 
Agassiz’s note, no work has given us much additional data regard¬ 
ing this most important point in the whole development. For the 
recent articles by Sars (’89) and Czerniavsky (’84) do not deal with 
the postzoeal stage except to depict the external form, although 
they are valuable records for several genera and species of hermit 
crabs. 
The present research, then, was undertaken in the hope that 
through a study of the anatomy from the time of hatching until the 
adult form was attained, and through examination of the role of the 
shell in the development, some knowledge of this almost untouched 
field might be obtained. The study was carried on during the three 
years prior to 1902 at Brown university and at the laboratory of 
the United States fish commission at Woods Hole. I wish to 
