128 THE VOYAGE OF H.M.S. CHALLENGER. 
The first pair are placed on the sides of the heart opposite to the second pair of legs; ° 
the second pair are placed similarly, but opposite to the third pair of legs; the 
third pair are found near one another at the posterior extremity of the heart. Through 
these three pairs the blood is admitted into the heart,’ while it leaves it through a large 
opening placed at its anterior extremity. No aorta or arteries arise from it. In the 
heart of the specimens in spirits of Nymphon robustum and some other species I 
observed a compact mass of blood-plasm, which ‘so totally filled up the cavity of the 
heart as to give, after having been taken out, an exact figure of its form. 
As to the blood-cérpuscles I only observed that they are, in Nymphon and Colos- 
sendeis, round and flat bedies with a distinct nucleus. However, I observed also more 
irregularly-shaped fusiform bodies, especially numerous in the cavities of the skin of 
Colossendeis (Pl. XVIII. fig. 1). With regard to their shape and dimensions there is no 
great conformity between the opinions of Cavanna and Dohrn ; however, it is only the 
study of fresh material that can finally settle such controversies.” 
6. Genital Organs.—About the testis of the Pycnogonids hardly anything is known ; 
and this cannot be wondered at when one considers that the true males were only dis- 
covered by Cavanna in the year 1875, the animals with swollen thighs described as males 
before that period being really the females. However, even Cavanna does not seem to have 
correctly identified the male organs, for he places them in the fourth joint of the legs. . 
Dohrn has been the first, and hitherto the only one, who has pointed out the true position 
occupied by the testis, “‘ Die Hoden liegen im Kérper der Pyenogoniden, nicht in den 
Beinen, und bilden dort jederseits einen Schlauch, welcher in jede Extremitiit seiner 
Seite einen kleineren Schlauch absendet, der an der obenerwihnten Stelle in einer runden 
Oeffnung endet.” This description, true in the main, is, however, not applicable to all 
the species of Pyenogonids ; for, from what I have observed myself, I am able to furnish 
full evidence that, for some species, Dohrn’s description is not quite correct. 
A large specimen of a male Colossendeis proboscidea, figured of the natural size in 
Plate XXI. fig. 10, has been opened on the dorsal side. The skin with the heart being 
removed, the testis is observed in situ, and the intestine may be distinguished below 
it ; the male organ, therefore, is placed rather at the dorsal side of the body. 
The two laterally and longitudinally running parts of the organ are united posteriorly 
1 From observations I made, in the summer of 1880, in the laboratory of Prof. Lacaze-Duthiers at Roscoff. 
2 Cayanna calls them “ piccolissimi globuli ellitici o sobellittici.”. Dohrn, on the other hand, describes the blood- 
corpuscles as “ungewohnlich gross und complicirt.” According to Dohrn, there are two forms of blood-corpuscles—“die 
einen bilden einen blassen, suzammengefalteten Ballon, in dem ein etwas gliinzenderer linsenformiger Kern sich findet 
neben 3—4 grossen Vacuolen; die anderen sind deutliche Amében, mit lebhaften amodboiden Bewegungen und 
umschliessen oder tragen eine gréssere Anzahl glinzender Trépfehen.” It seems to me that the iarge balloon-forming 
elements come very near to my fat cells (see p. 127) ; and as to the ameboid corpuscles, these are probably my fusiform 
elements and the elliptic ones of Cavanna, If Dohrn is right about his large blood elements, then the animals must 
have still others of a third form. 
