THOMPSON: METAMORPHOSES OF HERMIT CRAP. 199 
Although historical parallels are unsafe, it is interesting to note 
the essential likeness of the argument from relative size to one of 
the objections brought by Westwood (’35) against J. Y. Thompson’s 
assertion that the higher Decapoda developed through a metamorpho¬ 
sis. He said that he had collected “specimens of zoea that were ten 
lines long between the spines, .... far too large to suppose that 
they would subsequently put off their zoe form and appear as crabs, 
bearing at the same time in mind .... the minute size of the latter 
animals in the very young state, although possessing their ordinary 
form.” 
Similarly, the supposed rarity of the Glaucothoe is more apparent 
than real. When we remember that these forms were almost all 
collected at some depth below the surface, the number already taken 
— about twenty — does not seem especially small. And further, 
even among littoral Crustacea the larvae are often less abundant 
than would be inferred from the prevalence of the adults. The 
young of the lobster, Homarus, for example, swim freely for ten to 
twenty days after they hatch, but they are not commonly taken in 
tow nets. The glaucothoe larvae of the Pagurids themselves have 
seldom been recorded. The Plankton expedition of 1889 does not 
record a Pagurid zoea, and the glaucothoe phase is relatively much 
rarer than the zoeae. At Woods Hole, where hermit crabs are very 
abundant and the zoeae are obtained in unusually large numbers, 
fifteen or twenty glaucothoe would be an excellent haul for one day, 
and the average would be much lower than this without considering 
the days when the animal plankton is extremely scanty, although 
occasionally I have collected, on particularly favorable night tides, 
when there was a full moon, nearly or over a hundred glaucothoe. 
My research bears directly upon Bate’s suggestion (’68) that glau- 
cothoe-phase larvae probably continue in the form until they obtain 
a shell and perhaps moult and grow. Recently this theory has 
been elaborated by Bouvier (’91a) as directly applied to the Glauco- 
thoes themselves, in explanation of their size and rarity. “They 
are, so to speak, less fortunate larvae than the rest, which continue 
to grow until the time that they find a suitable habitation.” Now, 
I find in the genus Eupagurus a glaucothoe phase that comprises 
onlv one stage, during which there is almost no increase in size. 
The duration of this period is short and it is but little affected by 
delay in obtaining a habitation. These results are found to be fully 
