BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 27. AFD. IV. N:0 6. 19 



The germinal canals or tubes are bounded by a thin base- 

 ment-tnembrane, inside which are arranged the primary ger- 

 minal cells with their large rounded nuclei. These cells subse- 

 quentl}'- become converted into ova and spermatozoa. In the 

 neighbourhood of the genital basis, gronps of them protrude, 

 together with surrounding tissues, in order to form minute 

 knobs or club-shaped bodies, the first developmental states 

 of the future genital tubes (Pl. I, fig. 8 f.). Among the true 

 germinal cells, others are to be found characterized by a 

 smaller oval nucleus. These cells do not become converted 

 into ova and spermatozoa, but are follicular cells and probably 

 serve directly in the nutrition of the former. 



Consequently, the germinal cord is the matrix from which 

 not only the genital products but even the genital basis and 

 its tubes originate. 



The genital tubes. 



As before mentioned, the tubes shot out from the genital 

 basis, reach their greatest length behind, and shorten gradually 



The most anteriorly placed small club-shaped bodies representing the earliest 

 developmental stages of genital tubes. Highly magnified. 



forwards, in order to present themselves as very small, simple 

 club-shaped processes at the beginning of the efFerent duct. 

 Attention is also called to the singularity that a certain 

 number of genitfl tubes are male tubes, while another series 

 of tubes contains eggs and that the diiferent generations suc- 

 eessively alternate. 



It has been presumed that the genital tubes remain during 

 the whole life of the Holothurids, and that they retain their 



