128 THE VOYAGE OF H.M.S. CHALLENGER. 



The first pair are placed on the sides of the heart oj^posite 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 l:)lood 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 sjairits of Nijmjyhon rohiistum and some other species I 

 observed a com23act 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-corpuscles I only observed that they are, in Nymphon and Colos- 

 sendeis, round and flat bodies 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 Korper der Pycnogoniden, nicht in den 

 Beinen, und bilden dort jederseits einen Schlauch, welcher in jede Extremitat seiner 

 Seite einen kleineren Schlauch absendet, der an der obenerwahnten Stelle in einer runden 

 Oeffnung endet." This description, true in the main, is, however, not applicable to all 

 the species of Pycnogonids ; for, from what I have observed myself, I am able to furnish 

 full evidence that, for some species, Dohrn's description is not c[uite correct. 



A large specimen of a male Colossendeis prohoscidea, 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 Roscoflf. 



^ Cavanna calls them " piccolissimi globuli ellitici o sobellitticL" Dohrn, on the other hand, describes the blood- 

 corpuscles as " ungewohnlich gross imd complicii-t." According to Dohrn, there are two forms of blood-corpuscles — "die 

 einen bilden einen blassen, suzammengefalteten Ballon, in dem ein etwas glanzenderer linsenfomiiger Kern sich findet 

 nel)en 3^ grossen Vacuolen ; die anderen sind deutliche Amoben, mit lebhaften amoboiden Bewegimgen und 

 umschliessen oder tragen eine griissere Anzahl glanzender Trdpfchen." It seems to me that the lai'ge balloon-forming 

 elements come very near to my fat cells (see p. 127) ; and as to the amoeboid 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 stUl others of a third form. 



