30 M. Pli. Owsjannikow on the 



the area, and was so arranged that the sensory surface seemed 

 to dip away sideways under the cuticle of the claw, and could 

 then be followed under the microscope through the base of the 

 claw into the next joint. The lower ventral edge of the 

 exposed part of the sensory organ was protected by hairs 

 regularly arranged so as to slant over the delicate surface, 

 while dorsally, where the sensory surface disappears under 

 the cuticle, the slit-like opening is guarded by a regular row 

 of fine hyaline hairs, which rise from the sensory surface and 

 curve over the outer cuticle. Apparently similar hyaline hairs 

 can be focussed down in the lower parts of the invagination. 

 On both old and young curious hairs with heads like narrow 

 dentate leaves occur at each end of the sensory area*. 



The finer histological details of tliis organ in Phrynus can 

 only be made out in young specimens when the chitin is not 

 too thick for sectioning. I reserve further details of the organ 

 in Oaleodes for a comprehensive work which I am now pre- 

 paring on this animal. 



The presence of this presumably olfactory organ in such 

 different Arachnidan types as Oaleodes and Phrynus is of no 

 small interest. The clarified pedipalp of Scorpio showed no 

 trace of such olfactory organs. The same must be said of a 

 Chernetid, apparently an Obisium^ which had been boiled 

 in caustic potash. The pedipalp of a Telyphonus was 

 also searched in vain by clarifying rough sections. I 

 unfortunately had no young specimens of this latter at my 

 disposal. It seems to me not improbable that some traces of 

 such an organ might be found in very young animals con- 

 sidering the apparent affinity which exists between Phrynus 

 and Telyphonus. 



Whether the peculiar sexual organs at the end of the pedi- 

 palp of the Araneids had any original connexion with such a 

 sensory organ is a point well worth investigating. 



V. — On the Embryology of the River-Lamprey, 

 By Ph. Owsjannikow f. 



Modern methods, including both serial sections and also the 

 new staining reagents, now enable us to prosecute a much 



* As an index of the accuracy of Koch's figures, the position of this 

 organ is marked by a gToup of hairs in the drawing of Phrijnus ceylonicus, 

 plate 776 in vol. x. 'IJebersicht der Arachni den-Systems.' 



t Translated from the 'Melanges Biologiques tir^s du Bulletin de 

 I'Acad^mie Imp^riale des Sciences de St.-Pltersbourg ,' t. xiii. livr. i. 

 St. Petersbui-g, 1891 : pp. 55-67. 



