l*Vt S'OGOXIDA 



uliferous segment; Dohrn: das erste Rumpfsegment; I'.ohm: Augenring; 

 phalothorax Hansen: farste Kropring; Sars: Hovedsegment (seg- 

 ilicum). 

 Tin mi, when viewed Erom above, presents a simple surface without any bra« 



articulation, and Kroyer, when he nevertheless divides ii into an oculai segment and 

 segment of thorax, has not been able to point out any traci m 01 anj other arti- 



ition, but has evidently started Erom the a priori reason that eyes cannot be Found on a thoracic 

 [lowing). It' the animal, however, is seen Erom before, several seams or lines maj some- 

 tinii en nunc- 01 less distinctly, as marking the boundarj oi peculiar skeletal parts, originally 



independent, but now united with the first segment of the thorax. Thus under the fore-edge of the 

 ment of the trunk in Pallenopsis plumipes the common skeletal part (metamere) of the cheli- 

 111. i\ be seen a> a transverse band (pL I\', Kg. 3). To understand the first segment of the trunk, 

 it is quite necessary to follow the larval development from the embryo. It will then be seen that the 

 and foremost chief part of the embryo is formed by the proboscis and the three pairs of embry- 

 onal lim ninding this latter, while the other chief part is not developed till later, the ambula- 

 legs and the four segments of the trunk together with the caudal segment not being partitioned 

 off at first The first chief part, most frequently with the exception of the chelifori, shrinks by and 

 by, loses its independence of the other chief part, and is, as it were, swallowed up by the foremost 

 part of this latter, the first segment of the trunk; not until this has taken place, and the embryonal 

 have fallen off, do the imaginal fore-limbs, palpi and ovigerous legs, spring forth on the lower 

 of this segment, when they are developed at all. The further details of this growth will be 

 found in the following in the section treating of the larval development 



If we suppose that the four segments with the ambulators- legs of the Pycnogonida corresj 

 with the thorax of the other Arthropoda, especially with that of the Arachnida and Insects, and the 

 first principal segment of the embryo with its three pairs of limbs likewise corresponding with the 

 head of those animals, the name of Cephalothorax (Hoek, Adlerz) for the first segment of the 

 trunk would be very good; but as I consider this comparison as wrong, or, at all events, as inde- 

 monstrable, I shall prefer another, less marked appellation, and as such I consider the one I have 

 sen. I, for my part, think it to be most probable, or at all events possible, that the second princi- 

 pal segment of the Pycnogonida with its four pairs of ambulatory legs and the caudal segment can 

 red with the abdomen of the Arachnida, in which this part in its development has, or may 

 have a similar division into somites, and similar rudimentary limb-, as in the I\ cuo^onida, cp. L-ocy: 

 ■ii. Agelena, 1885, pi. II, fig.9 11, and pi. Ill, Kg. 13 15. The position of the genitals then 

 won rally is the case, be in the abdomen, and in the processes of the abdomen, that is, 



the ambulat 1 »n the other hand, the eves would be placed on the fore edge of the abdomen, 



but ■ in the pedunculated Crustacea) do not form a typical part of the body in 



animal, belonging to or constituting the head; and even if we, to avoid this difficulty, should call 

 the ■ , in which the eyes are placed, cephalothorax, it is still in the hindmost part of 



this segment, in the thorax, or the first somite of it that the eyes would be placed and farther 

 itself, they would never come. 



