PYCNOGONIDA. 29 
disappeared second pair of embryonal legs, which is then marked as 3 I in his figures, pl. 16 and 17, 
fig. 3—12. If Semper had known the development of more Pycnogonid-larvæ, his explanation would 
immediately have appeared impossible to himself. 
Morgan, Contrib. Embryol. 1891, has found in 2a//ene empusa, p. 24 seq. the same development 
as I have found in my two species of that genus. I dare not, however, say of the development of 
the three foremost pairs of ambulatory legs that it is «simultaneously», even if the interval between 
the second and third pair is only small, as has been already observed. Nor can I, as is seen by the 
foregoing, agree with Morgan as to the fact that «this third pair (i.e. the rudimentary embryonal 
legs) grow out again to form the ovigerous legs». Finally I do not find that FPa//ene with Pseudo- 
pallene deviates so much from the ordinary Pycnogonid-development, that there is sufficient reason to 
finish, as does Morgan, the description of its ontogeny in the following way: «The development of 
Pallene has become so much abbreviated that there is only a trace of the true Pantopod-larva found 
in its ontogeny», cp. the foregoing. 
Dohrn, Bau u. Entwickl. Arthrop., 1870, p. 144—51, gives a detailed description of Åchelia 
(Ammothea) lævis, and in pl. VI, fig. 11—13 he draws three consecutive «stages» of the development 
of this animal, of which three stages I refer his first (in the explanation of the plates called «< mittleres 
Stadium») and second stages to my second stage. In the corresponding figures, fig. 11 and 12, the 
embryonal legs are still seen fully developed, with the exception that the last pair in fig. 12 are some- 
what smaller than the other embryonal legs; but judging by my examinations, I regard the smaller 
size, cp. also my fig. 24 on pl.I, as a consequence of the fact that only the empty sheaths are left, 
and that besides the points or outermost joints of these sheaths, as in my figure, are retracted, partly 
into the preceding joint; I cannot suppose a reduction or real diminution of this pair of legs to have 
taken place. — Also the larvæ given by Dohrn, Pantop. Golf. Neap. 1881, pl. XI, fig. 21 and 24, and 
determined as -hoxichilus vulgaris, must be referred to our second larval stage; but the specific 
determination, especially with regard to the last figure, seems to me to be very doubtful. The first 
figure, fig. 21, represents a normal Pycnogonid-development, in which I only think it to be not very 
probable that a -xoxichilus should have kept its chelifori so long, and not rather have lost them, 
either by reduction or throwing off, while the nearly related Pycrogonum has wholly lost them before 
the close of the stage, cp. my figure, pl. I, fig.4.. The improbability that Phoærchilus should have 
kept the chelifori so long, is of course greater with regard to the older larva, fig. 24, Pycrogonum 
having lost them on a little earlier stage. But I am still more unable to believe that the imaginal 
fore limbs, of which only the hindmost pair are developed and kept only im the male, should commence 
and begin a development which was soon to be stopped or reduced; for I think it a fact that admits 
of no doubt, that the appendages, marked in fig. 24 with II and III, are not rudimentary, reduced 
remnants of the embryonal legs, but on the contrary a beginning development of the imaginal 
fore limbs. 
The third larval stage begins, when the fourth pair of ambulatory legs, which 
have until now been far behind in development, together with the interjacent caudal 
segment, begin to grow and develop, until they obtain their permanent shape, the 
legs resembling the three foregoing pairs. The imaginal fore limbs, palps, and ovi- 
