LIMULUS AN ARACHNID. 535 
ture of this deep skeletal tissue has been investigated by 
Gegenbaur, who has shown that it may have the form 
either of a fibrous or of a more distinctly cartilaginous 
modification of the connective tissue into which it gradu- 
ally passes, and from which, on the other hand, is developed 
in other regions a series of vascular channels constituting 
the capillaries, veins, and arteries. On the present occasion 
I do not propose to enter into histological details with 
regard to Limulus, but I may just mention that whilst the 
hollow entapophyses are invested on their visceral surface 
by a richly developed cartilaginous modification of the con- 
nective substance, with a well developed capsular arrange- 
ment of the intercellular substance, the funnel-like invagi- 
nations connected with the parabranchial stigmata are 
clothed and continued by a fibrous tissue not unlike the 
tendon of Vertebrata. The same tendon-like tissue also 
forms the entosternite. 
In Plate XXVIII, fig. 11, the internal connection of the 
pair of parabranchial stigmata of a lamelligerous appendage- 
pair of Limulus is drawn. The integument has been dis- 
sected away from the whole of the anterior face of the 
appendages and their uniting sternal bridge, so as to show 
the inner aspect of the integument of the posterior face. 
The pouch-like character of the invaginations into which 
the stigmata lead and the attachment of the thoraco- 
branchial muscle is thus exhibited. In fig. 18, PI. 
XXVIII, one of the funnel-like tendons, consisting inter- 
nally of chitin borne on epidermis, and externally of fibrous 
tissue, is shown in an isolated condition. It is possible to 
introduce a probe into the funnel to the depth of an inch, 
the axial cavity of invagination extending to that distance. 
The funnel-like pouch of Limulus thus constituted, I con- 
sider to be the homologue (that is, the genetic representa- 
tive or homogen) of the pulmonary sac of Scorpion. 
It will now be convenient to give, in a tabular form, a sum- 
mary of the view which has been set forth in the preceding 
pages. Having thus exposed what I conceive to be the legiti- 
mate conception of the morphological relations of Limulus 
and Scorpio, I shall endeavour to justify, by a closer 
examination, the identification (which forms an essential 
part of it) of the pectines of the Scorpion and its four 
pairs of book-like organs sunk in recesses of the integu- 
ment with the five pairs of lamelligerous appendages of 
Limulus. 
(The tabular statement is given on the next page.) 
