MEMOIRS OF TOE ^JATIONAL ACADEMY OF SCIENCES. 371 



The majority of the ilecap(»(l (Jnustawii have a Um>^ and coni|>licatc.tl metamorphosis. That 

 ill a few forms the early stajjes are jiimpeil, so tiiac the yoiiiij; hatch in pnicticaily the adult coudi- 

 tion, is a remarkable fa(!t,'aiid the discovery of a probable cause for this phenomenon in ^pbeus 

 is one of the most interestin<,' results of that part of our work which deals with the metamorphosis 

 of the genus. 



The development of Alpheus has never, I believe, been previously studied, excepting the 

 metamorphosis of the two I'.eanfort species, so that there is no work of others to refer to, which 

 bears directly upon our subject. I!ut tiie literature of the Arthroiiods is very great, comujensurate 

 indeed with the size of the group. During the |>roges8 of this work a number of imi)ortant papers 

 have appeared which are referred to either in I he text or in n«)tes. While much is known of tbe 

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

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

 nature. There is great need for detailetl and full accounts of the dev»',lopment and organogeny 

 of many forms in 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 sup[)lyiug the need just men- 

 tioned, but how imperfectly it is unnecessary to say. 



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

 studies of Ali)heus has been as yet only partially carried out. The early stages of ISlcnopus hispiduH, 

 Homariis Americanus, and Pontonia domeatica have, however, been followed, and less completely 

 those of Hippa talpoides and PaUtmonetes vith/drii,: 



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

 memoir, with drawings, communicated to the Royal Society in 187C, from a specimen procured in 

 the Mauritius, lie named his s|)eciinen Ilomarnlpheus, ''from the impression that species producing 

 a Megalopa could not be placed in same genus as those producing a Zoea." He says: "The orig 

 inal of my drawing is 2""" in length and was i)rocured from a specimen 14"""' long, resembling the 

 figure that I have given oi Alpheus minvn, Say. An iusi)ectiou of this drawing (3, PI. oxxii. Fig. 1 ) 

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

 general shape is unlike that of Al[)heu8, the abdomen being three times as long as the carapace, 

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



I'ackard (40) in 18SI was the first to describe a shortened metamorphosis for Alpheus hetcrochelis. 

 In some brief notes ])ublislied in the American Naturalist of that year, he states that both this and 

 the small green Alpheus (yl.»ji«H.s) occur in abundance at Key West, Florida, in theexcurrent open- 

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

 shown. Packard descril)es tlie 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 Bahamau Ali)beus soon to be described, 

 in which the metamorphosis is nearly lost. 'The Nassau t'orin of Alpheus hcterochelis has, as I have 

 recently ascertained, a eomplete 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 in 1882. This is all, I believe, that has been [jreviously done 

 on the embryology of these Crustacea. Several abstracts of the present work appeared in 1887-'88 

 (20-22). 



METHODS OF WORK. 



Several species of prawns, such as Stcnopus 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 

 pha?fes of develoi)ment, and were kept under observation in an aquarium for the length of time 

 required. The ova were then carefully removed from the pIeopods,aiid were hardened at intervals of 

 thirty minutes or one hour or a longer time, according to the phase or age of the eml>ryo. By obtain- 

 ing i^number of series in this way the whole life history within the egg could bo followed, and by 



