366 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



fuuctiouless. Careful examination shows that there are tive pairs (the five pairs of thoracic limbs), 

 ami that all but the last pair are biramous. In all, the exopoilites are longer than the cndopodites, 

 which decrease in length from in front backwards, while the eudopodites increase in length. The 

 later history of these limbs shows that the exopodites never become functional, aa they do in the 

 Bahama form. 



All six abdominal somites are distinct, although the line separating the sixth from the telson 

 is faintly marked. The first five pairs of abdominal feet are represented by five biramous buds 

 projecting beyond the outline of the body, while the sixth pair are only faintly outlined under the 

 cuticle of the telson, which itself presents a most important difference from that of the young 

 Bahama larva, as it is not triangular, but spatnlate ; and of the eight pairs of setaj the three pairs 

 which in Al/iltcnK minor He on the lobe at the angle of the telsou are not on a distinct lobe, nor do 

 they differ in size from the adjacent seta?. 



This larva, molts a few hours after hatching, and at once undergoes the most profound changes, 

 and assumes the form shown in PI. xx, Fig. 3. It is no longer a larva, but a young Alpheus. 

 The eyes are almost covered by the carapace, the car is well developed, and all the, appendages are 

 present and functional and essentially like those of the adult. The autennule has two Hagclla, each 

 with several joints. The flagellutn of the antenna is more than twice as long as the scale ami is 

 composed of twenty-two joints, while the scale has -its final form. 



The first maxilla (Fig. 5) has a large club-shaped lobe, fringed with short hairs, and a rudi- 

 mentary eiidopodite, while the second maxilla (Fig. (>) is a broad flat plate with cutting lobes and a 

 short, rod like endopodite. The three pairs of maxillipeds (Figs. 7, S, and 9) have assumed the char- 

 acteristic Macrourau form and are no longer concerned in locomotion, while the thoracic limbs have 

 elongated into the tive pairs of ambulatory appendages of the adult, although they still retain 

 their rudimentary exopodites. The abdomen is now like that of the adult, and the telson (Fig. 

 4) is long and narrow. An older specimen is shown in Fig. li and a still older one in PI. xvn, Fig. 3. 



Comparing the history of the Bahama form with that of the North Carolina form, the most 

 conspicuous peculiarity, aud that which first attracts attention, is tl.e great abbreviation of the 

 latter. The Beaufort specimens hatch in a much more advanced condition than the Bahama speci- 

 mens, and, while the latter pass through many larval stages, the former quickly assume the adult 

 form. This is not all, nor is it even the most fundamental difference between them. The develop- 

 ment of the Beaufort specimens is not simply accelerated; it is profoundly modified, so that nc 

 exact parallel can be drawn between any larval stage of the one and a stage of the other. The 

 statement that the Ueaufort specimens pass, before leaving the egg, through stages which are 

 exhibited during the free life of the Bahama specimens would do violence to the facts; for the 

 difference between them is very much more fundamental than this statement would imply. For 

 example, the Bahama form has at first three, then four, then five, aud then seven schi/.opod feet 

 with functional swimming exopodites, while the Beaufort form never has more than three. As 

 regards the thoracic region aud the first five abdominal appendages the Beaufort larva, at the time 

 of hatching (PI. xrx, Fig. 1), is more advanced than the fourth larval stage of the Bahama form 

 (PI. xvm, Fig.;-!), while the sixth pair of abdominal appendages are like those of the Bahama form 

 at the time of hatching ( PI. xvi, Fig. 3). In the Bahama form the first and fifth thoracic limbs are 

 the oldest, and the others appear in succession from in front backwards ; all live pairs make their 

 appearance together in the Beaufort form. In the Bahama form the sixth pair of abdominal feet 

 appear before and in the Beaufort form alter the others. Many minor differences of the same 

 general character show that we have to do with profound modification of the life history rather 

 than with simple acceleration. 



THE DEVELOPMENT OF ALPHEUS HETEKOCHELIS FROM KEY WEST. 



According to Packard's account the specimens of ,1 l/ikcx n Jit-terochi'lin which occur at Key West 

 differ from those which occur at Beaufort in about the same way that the latter differ from those 

 from the Bahamas, as the metamorphosis appears to be entirely absent in the Key West speci- 

 mens. Packard states that, while still inside the egg, they had all the appendages of the adult 

 in essentially the adult form. There were tive pairs of thoracic legs and the first pair had large 



