200 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
a quadrangular plate, about two-thirds as broad as long, with, an even convex margin 
bordered with long fringing setae at its binder end. The median spine bas disappeared 
and tbe long lateral spines are reduced to short, stout teeth. 
In the later adolescent stages the fringing setae of the caudal-fan become greatly 
elongated until they nearly equal the telson in length. The adult telson is somewhat 
spatula-shaped and about as broad as long at its base. 
THE METAMORPHOSIS OF HOMARUS GAMMARUS. 
Sars studied the first three larval stages of the European lobster in specimens 
which he collected at the surface of the ocean. He saw enough to convince him that 
they were at this time an easy prey to fish, swimming birds, and to ocean currents 
which swept them into unfavorable places (175). 
At Espevaer, a fishing-place on the coast of Norway, his attention was directed to 
large numbers of lobster larvae, which were there u packed together with an enormous 
mass of Calanides (a kind of herring) and other species of pelagic animals, upon which 
swarms of herring and birds were feeding.” 
The abbreviation of the metamorphosis has been carried a little further in Romanis 
gammarus than in the American species. The young of the two forms apparently agree 
in color, but are very dissimilar in size. According to Sars, the first three larvae of 
the European lobster measure 10, 14, and 17 to IS mm., respectively. If these meas- 
urements are representative, the first larva of this species is larger than the second 
larva of Romanis americanus , and the third larva larger than the sixth stage. (See 
table 25.) 
The color of the third larva, according to Sars, is a mixture of yellow-red or brown 
and blue-green, and at this stage the integument has lost much of its transparency. 
The carapace, the large chelipeds, and abdomen in the first larva of the European 
species have reached a stage of development which corresponds very nearly to the 
second larval stage of the American form. This is best illustrated by the rostrum, 
large chelae, and telson. The second somite of the abdomen is devoid of the median 
spine, which, as we have seen (table 36), usually disappears in the American form 
with the second molt. Sars says that even in the first stage the anlage of the uropods 
can be discerned beneath the cuticle. These appendages, however, are not released 
until after the third molt, as in our lobster. 
THE SHORTENING OF THE METAMORPHOSIS IN THE LOBSTER. 
I have discussed in my work on the development of Alpheus (94, p. 380) the 
abbreviation of the larval period in Crustacea, and described the remarkable exam- 
ples of this phenomenon which the study of the Alpliei revealed. We will now consider 
the case of the lobster a little more closely than it was possible to do at that time. 
What is the cause of the suppression of the zoea stage in the metamorphosis of this 
animal f 
We can not doubt that this is a secondary phenomenon which has appeared in 
comparatively recent times, and that some of the immediate ancestors of the lobster 
went through the long metamorphosis after hatching, as the majority of Decapods do 
to-day. It is equally certain that something in the environment of these animals has 
called forth this change. Why should the lobster be better off with a short metamor- 
