32 PYCNOGONIDA. 
number of homologous limbs in the Arachnida is six pairs, but in the Pycnogonida seven pairs. But, as I 
have already tried to show in the foregoing, the seven pairs of limbs in the latter animals are not all reciproc- 
ally homologous, and the typical number of pairs is not seven, but nine. Of these nine pairs of limbs 
especially the four last pairs, the ambulatory legs, are not at all homologous with the ambulatory legs of 
the Arachnida, but in all likelihood with the four pairs of small processes that have been pointed out in 
the abdomen of the Arachnid-embryo, cp. Balfour, Notes on the Development of the Årarerma, 1880, and 
Locy, Observations on the Development of Åge/ena nævra, 1886. Both the mentioned authors represent four 
pairs of distinet beginnings of limbs arising from the abdomen of an embryo of an Age/ena, Balfour, 
1.c. pl. XIX, fig. 5—8 pp. or pp. 1—pp. 4, of Ag. /abyrinthica, and Locy, 1.c. pl: TIV, fig. 711, 1314, 
20—21 pr. app. of an Ag. nævia. These beginnings which may reach a rather considerable length, 
are by Balfour called «provisional appendages», a name also adopted by Locy. On the other hand, 
I know of no instance of the genitals or their excretory duets in any Arthropod being found in the 
thorax or the limbs of this part, as would be the result of the common interpretation of the ambu- 
latory legs of the Pycnogonida. 3) Furthermore we find im the Pycnogonida an organ so decidedly 
of the Arachnid-type as the chelifori, with which also join 4) the embryonal byssus-glands, a 
homologon of the poison-glands of the Arachnida. The want of particular respiratory organs gives 
no information with regard to systematism, but it may be said to point to an origin or development 
from primitive, larve-like forms. 5) Finally the presence of «auxiliary claws» (i. e. real claws) is an 
important feature in the Arachnida in contradistinction to the Crustacea. 
Relying on the points given in the foregoing, I think myself justified in classing the Pycnog- 
onida among the Arachnida, as a group which with regard to the outer appearance is very much 
deviating, as it has also become very strange by a strong development of organs that in other Arach- 
nida are only begun, or have been reduced, and upon the whole adopted to the life in the water, 
especially the sea. 
When we next pass to the inner systematism of the Pycnogonida, or the consecutive order 
of the species, we shall first have to consider that the species, as far as they are known, form a close 
and united series of forms, so that there can be no question of dividing them into different groups, 
corresponding to the division into orders in the animal world in general, or in the Arthropoda in 
particular. Even if we should follow the common notion, and consider these animals as having their 
place outside the acknowledged four classes of Arthropoda, they would not for that reason become a 
fifth class of the same rank as the other classes, nor will it be necessary to divide them into a smaller 
or greater number of orders, suborders, families, subfamilies, genera, subgenera, species, and subspecies. 
Corresponding frames may of course easily be put up, and have partly been put up; but then when 
the animals are to be classed according to such frames, these frames soon appear to be quite artificial, 
as many species may be placed as well at one place as at the other. Therefore we also see, how the 
same species is, by different authors, referred, now to one genus or family, now to another, or even 
to different so-called orders. The genera and families, of course, are still less decidedly fixed, but 
change their position in a way and to an extent, unknown or inconceivable inside the class of Insects. 
With a common larval type and common larval development, as it has been shown in the section on 
the larval development, the orders and families that have been put up, have in reality only been 
