No. 1.] VARIATIONS IN LIMULUS POLVPHEMUS. 39 
certainly absent, because the cephalic lobes and abdominal ap- 
pendages are in their proper relative positions, and yet only 
three out of the six thoracic segments are present. It cannot 
therefore be argued that because in Fig. 62 the oesophagus 
lies just in front of the first pair of remaining appendages, 
that they are the original first pair and not the fourth. 
Figs. 33, 34, 35, 65, 66 probably represent modifications 
of this three-legged form in which the appendages have 
undergone various modifications through invagination, median 
fusion, and degeneration. 
In Fig. 34, the last pair have fused to form a median 
appendage, and in Fig. 35 there has been such distortion and 
reduction that it is hard to recognize what remains, but it 
appears to consist of the three left thoracic appendages and one 
right. The oesophagus lies at ve., and the telepore at &., at 
the bottom of a furrow partly covered by a hood-like fold. 
In most of these small three-legged forms, the median ventral 
surface is deeply depressed and closely surrounded by a thick 
and high marginal fold. 
III. MuvLTIPLICATION OF APPENDAGES. 
Multiplication of definite regions or organs of the body, not 
including in this category double or triple monsters, is very 
rare. JI have observed but one case. It is interesting and 
important, since it proves conclusively that a half of a metamere 
already laid down has the power to multiply independently of 
adjacent organs. This is shown in Pl. II, Fig. 12, where the 
right chelicera— which fortunately can be identified here with 
absolute certainty has divided twice. The first division 
apparently gave rise to a’** and a***. A subsequent division 
separated completely a? from a*. But the third division 
effected only a partial separation of a‘ froma’. The abnor- 
mal growth has also modified the right nerve-cord at this 
point, throwing the head over to the left. None of the 
neuromeres are very clearly brought out in this preparation, 
so it is not certain whether there is one for each of the four right 
chelicerae or not. But there is a prominent enlargement of the 
