366 MEMOIRS OF THE NATIO^STAL ACADEMY OF SCIENCES. 



functiouless. Careful exaiuiuatioii sbows that there are five pairs (the tive pairs i>l' thoracic limbs), 

 ami that all but the last pair are biramoiis. In all, the esopodites are longer than the eiiilopoilites, 

 which decrease iu leugth from iu front backwards, while the eudopoditcs increase iu length. The 

 later history of these limbs shows that the exopodites never become functional, as 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 biramons buds 

 projecting beyond the outline of the body, while the sixth pair are oidy faintly outlined uuder 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 si)atulate ; and of the eight pairs of set:e the three pairs 

 which in Alphcu.s minor lie on the lobe at the angle of the telson are not on a distinct lobe, nor do 

 they differ iu size from the adjacent setie. 



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

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

 The eyes are almost covered by the carapace, the ear is well developed, and all the ajipeiidagesare 

 present and functional and essentially like those of the adult. The antennule Ijas two fiagella, each 

 with several joints. The tlagellum of the antenna is more than twice as long as the scale and 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 endopodite, while the second maxilla (Fig. 6) is a broad flat plate with cutting lobes and a 

 short, rod like endopodite. The three pairs of maxillipeds ( Figs. 7, 8, and 9) have assii ned the cliar- 

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

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

 their rudimentary exo[)odites. 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. 2 and a still older one in I'l. xvii. Fig. 3. 



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

 conspicuous peculiarity, and that which first attracts attention, is the great abbreviation of the 

 latter. The Beaufort s[)ecimeus hatch in a much more advanced condition than the Bahama si)eci- 

 meus, 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 S[)ecimens is not simi)ly accelerated; it is profoundly modified, so that nc- 

 exact parallel can be drawn between any l4rval stage of the one and a slage of the other. The 

 statement that the Beaufort 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, and then seven schizopod feet 

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

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

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

 (PI. XYiii, Fig. 3), 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 iu succession from in front backwards ; all five 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 after 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 heterochelis from Key West. 



According to Packard's account the specimens of Alpheus heterocheUx which occur at Key West 

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

 from tlie Bahamas, ;is the metamorphosis appears to be entirely absent iu 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 five pairs of thoracic legs and the first pair had large 



