152 Miscellaneous. 
Evidence of a Protozoéa Stage in Crab Development. 
By H. W. Conn*. 
There is great interest attached to speculations as to the probable 
ancestry of the Decapods, owing to the value which the conclusions 
have in enabling us to interpret paleontological facts. There have 
been quite a number of theories advanced as to the original stem 
from which the Decapods have been derived, two of which claim 
especial attention. One is the theory of Miller, who finds such a 
stem-form in the zoéa. Another, suggested by Glaus, or in a diffe- 
rent form by Brooks, considers the protozoéa as the ancestral stem. 
It is of great importance in understanding the Crustacea to decide 
between these two views, inasmuch as by the first view Crustacea 
are supposed to have descended from a form without a thorax, while 
according to the second, the thorax was present in the original 
Decapod stem. Some work done at Hampton during the last summer 
upon the larval cuticle of crabs indicates conclusively that the latter 
view is the correct one, or that at least Fritz Miiller’s view is in- 
correct. The larval skin, particularly the telson, of a large number 
of crab zoéas was studied with the following results :—The larval 
skin is not in different crabs alike, nor is it in any case exactly 
similar to the enclosed zoéa. There is always an indication, more or 
less complete, of some previously existing stage. There has been 
shown in the various forms studied a gradation from the larval skin, 
with little difference from the zoéa enclosed, to a larval skin which 
is utterly unlike the zoéa, but which possesses a forked tail with 
fourteen long feathered spines. This gradation is complete, and a 
study of the different embryonic telsons shows that all have been 
derived from the form shown by Panopeus, which has a forked tail 
with fourteen spines. Now such a larval skin is to be considered 
simply as the cast-off skin of some stage immediately preceding the 
zoéa. It has been shown by Paul Meyer that the study of the larval 
skin of Macrura leads to a similar result; that a forked tail with 
fourteen spines is also seen in the early history of this group. If 
therefore a form can be found which shows these peculiarities, we 
have reason for accepting it as the stem-form of the higher Crus- 
tacea. Now a study of the different. protozoéa-forms which occur in 
the ontogeny of various Macrura shows that we have in this form 
a stage which fulfils the conditions. It has the forked tail with 
fourteen spines, and has large swimming antenne, another pecu- 
liar characteristic of the crab larval cuticle. If the various larval 
skins of crabs and Macrura be compared with each other, it will be 
seen that they are all to be ccnsidered as modifications of a tail 
much like that present in the larval skin of Panopeus; and if this 
tail be compared with the protozoéa-tail of Peneus, the likeness will 
be seen to be very striking. We have therefore, in the comparative 
study of the larval cuticle of crabs, good reason for accepting as the 
stem-form of the Decapods a form which had resemblance to a pro- 
tozoéa.—Johns Hopkins University Circulars, Jan. 1884, p. 41. 
* Abstract of a communication to the University Scientific Association, 
November 7, 1888. 
