388 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



are not prepared to answer these questions as fully as we could wish, yet the facts are sufficient 

 to throw some light upon the subject. 



We have abundant evidence that there is considerable fluctuation in the life of the individual, 

 as regards the number, color, and shape of pigmentcells for instance. In all larvre of these prawns 

 the external antenna; have a well developed scale, and it is thus clear that this organ may degenerate 

 and apparently disappear, to be reconstructed again at a later period. The variety Jinif/icurpiis (No. 

 15, Table I) has no " squanie," although it is present in the young (Fig. 7, PI. xxn), and the cases in 

 which the organ is seeu in various stages of development (Figs. 13, 14, PI. xxii) support and illus- 

 trate this conclusion. This, however, is not a rule with the species as a whole, as it is in the some- 

 what analogous case of the loss and subsequent reconstruction of the last two pairs of thoracic 

 legs in the larvre of Steuopus and Sergestes. 



The question as to how far the characters which distinguish such forms as Nos. 1 and 15, Table 

 I, are congenital can only be answered by a careful study of their development. My attention was 

 not directed to this subject while at the seashore, and in this connection some interesting experi- 

 ments remain to be performed. The evidence we have goes to show that the young in any given 

 case share the peculiarities of the mother, and this is probably true of such details as the, right and 

 left handed condition of the large chelipeds. The following examples illustrate this fact: (1) The 

 adult female in this case has the characters of No. 15, Table I. The autennular or aural spine is 

 nearly three-fourths the length of the first antenuular segment. The aural spine has a correspond- 

 ing length in the larva} of this prawn at the time of hatching. In the adult the fingers of the 

 small chela end in prongs; there is a tuft of peculiar setse on the dactyle. In the first larva the 

 fingers of the small chela also end in prongs, and there is a tuft of rudimentary setn- on the dac- 

 tyle. In the adult the carpus of the small cheliped is relatively very long. In the first larva the 

 carpus of this appendage is about one-third the length of the propodus (relatively a little shorter 

 than in the, adult). Fig. 11, PI. xxn, may be taken to represent the mother (rostrum here wanting), 

 and Fig. 17 the youug. The small chela of the mother is shown in Fig. 2, PI. xxiv, that of the young 

 in Fig. L">, PI. xxti. Another case exactly like this was observed, where the embryo was taken 

 from the abdomen of the female. (2) The adult in this case has the characteristics of No. 2, Table 

 I (var. brericarpus) (PI. IV, Figs. 1, 2). The larva? are shown in PI. xxi, Figs. 1, 2, 3, 8. The aural 

 spine, at first short, is nearly as long as the first anteunular segment when the larva is a week old 

 (Fig. 10, PI. xxii). In both the parent and young the carpus of the small cheliped is relatively 

 short. The lingers of the small chela end in simple tips; there is no tuft on the dactyle (see 

 Fig. 16, PI. xxii). 



These facts indicate that the young share the peculiarities of the parent, but exactly how far the 

 individual may depart from this standard in its own life, or how strictly the law of inheritance 

 applies in all cases, my observations do not warrant a decisive answer. A few experiments could be 

 easily made upon this Alpheus which would throw light on some inteiesting questions in heredity. 

 The females with ova are easily obtained; the young are readily hatched and kept alive in glass 

 dishes until they have reached the adult state. 



In this species the change of environment, due to the adoption of life in sponges, has probably 

 aeted as a direct stimulus to variation. These auimals tend to vary most along certain definite 

 lines, as, for instance, the relative lengths of the, antennular segments and aural spine vary much, 

 while those of the segments of the carpus of the second pair of thoracic legs are practically invari- 

 able. Homologous pa^ts vary alike, unless specially differentiated in different ways, as in the 

 chelipeds. There is no diversity of life between males and females, and both sexes vary alike, but 

 aberrant males are probably the more common. 



The occurrence of large numbers of individuals showing variations of the same kind, but of 

 different degree, render it plausible at least that the same variations may occur in a large number 

 of individuals simultaneously, but the reason why this or that part has varied most is wholly 

 obscure. 



The aberrant forms (variety longicarpus) which have adapted themselves to life in the brown 

 sponge thrive and produce young which, in the early stages certainly, share in the peculiarities of 

 the parent. The variety brevicarpus is similarly adapted to its environment and its young resemble 



