MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 371 



The majority of the decapod Crustacea have a long and complicated metamorphosis. That 

 in a few forms the early stages are jumped, so that the young hatch in practically the adult condi- 

 tion, is a remarkable fact, and the discovery of a probable cause for this phenomenon iu Alpheus 

 is one of the most interesting results of that part of our work which deals with the metamorphosis 

 of the genus. 



The development of Alpheus has uever, I believe, been previously studied, excepting the 

 metamorphosis of the two Beaufort species, so that there is no work of others to refer to, which 

 bears directly upon our subject. P>ut the literature of the Arthropods is very great, commensurate 

 indeed with the size of the group. During the progess of this work a number of important papers 

 have appeared which are referred to either in the text or in notes. While much is known of the 

 Arthropods as a whole and of that large division of them included under the Crustacea, it is 

 probably true that a great deal of this knowledge is of a very fragmentary and unsatisfactory 

 nature. There is great need for detailed and full accounts of the development and organogeuy 

 of many forms iu order that the relations of the various members of the Arthropod type may be 

 clearly established. 



The present work may be regarded as a contribution toward supplying the need just men- 

 tioned, but how imperfectly it is unnecessary to say. 



The plan of making observations upon other Crustacea for comparison with the more detailed 

 studies of Alpheus has been as yet only partially carried out. The early stages of Nlenopun hispidm, 

 Romania Americanus, and Pontonia domestica have, however, been followed, and less completely 

 those of Hippa talpoideis and Palannonetex rulij/iria. 



Spence Bate (3) states that the shortened development of Alpheus was first described in his 

 memoir, with drawings, communicated to the, Royal Society in 1870, from a specimen procured in 

 the Mauritius. He named his specimen Hamaralpheus, "from the impression that species producing 

 a Megalopa could uot be placed in same genus as those producing a Zoi'-a." He says: "The orig- 

 inal of my drawing is Li""" in length and was procured -from a specimen 14 mm long, resembling the 

 figure that I have given of Alplti'i/s minim, Say. An inspection of this drawing (3, PI. cxxil, Fig.l) 

 leaves some doubt as to whether there was not an error in referring this form to the genus. The 

 general shape is unlike that of Alpheus, the abdomen being three times as long as the carapace, ' 

 and there appear to be only three pairs of thoracic appendages behind the chelipeds. 



Packard (40) in 1881 was the first to describe a shortened metamorphosis for Alpheux hrtcrochelis. 

 In some brief notes published in the American Naturalist ot that year, he states that both this and 

 the small green Alphens(A.7Kt/ms)occuriu abundance at Key West, Florida, in the excurrent open- 

 ings of large sponges. This fact is interesting, and probably significant also, as will be later 

 shown. Packard describes the first larva of this Florida form as much further advanced toward 

 the adult state than is the first zoea of the Beaufort species, according to the observations of 

 Brooks. In fact it more nearly agrees with the first larva of a Bahaman Alpheus soon to be described, 

 in which the metamorphosis is nearly lost. The Nassau form of Alpheux lietcnx-lielin has, as I have 

 recently ascertained, a complete metamorphosis. The bearings of these facts will be discussed 

 further on. 



The larval "development of the Beaufort Alphei was studied by Brooks (7) and a short 

 abstract of his results was published iu 1882. This is all, 1 believe, that has been previously done 

 on the embryology of these Crustacea. Several abstracts of the present work appeared in 18S7-'8S 

 (20-22). 



METHODS OF WORK. 



Several species of prawns, such as Stenopus and Pontonia, repeatedly laid eggs while kept in 

 aquaria, and doubtless I should have succeeded equally well with Alpheus, if sufficient pains had 

 been taken. As it was, only two or three individuals gratified me in this respect, but in each case, 

 the ova failed to develop. The animals were therefore taken from the sea with eggs in the earliest 

 phases of development, and were kept ittider observation in an aquarium for the length of time 

 required. The ova were then carefully removed from the pleopods, and were hardened at intervals of 

 thirty minutes or one hour or a longer timr, according to the phase or age of the embryo. By obtain- 

 ing a number of series in this way the whole life history within the egg could be followed, and by 



