660 JOHN BEARD, 



have, of course, never been seen, they doubtless possess considerable 

 powers of motion in an amoeboid fashion (as: e. g. in Hydra etc.). 



Indeed, the similarity of many of these cells to Amoebae is 

 very striking. Even in the immediate neighbourhood of the germinal 

 nidus one finds them in evident movement, while in many, many in- 

 stances they are encountered between splanchnopleure and gut in the 

 early embryos (Fig. 28), and in the later ones within the connective 

 tissue of the mesentery. 



In Fig. 34 one is even depicted in the act of making its way 

 through the splanchnopleure into the body-cavity. And the undoubted 

 germ-cell of Fig. 22 was found in three consecutive sections immediately 

 under the epiblast and just beneath the segmental duct in an embryo 

 of 10.5 mm. The nuclei are not always easily found, and this is 

 largely due to the yolk. Sometimes they are large, clear bodies with 

 a well-defined nucleolus. Nuclei of this kind are most commonly 

 found in the germ -cells of older embryos. In early embryos they are, 

 where well seen, very frequently if not always, of a bilobed or twin 

 nature — a remarkable character of primary germ-cells, recorded in 

 Arthropods by Rückert ('95) and Hacker ('96), and now shown to 

 characterise the very early germ-cells of Vertebrates. 



We now approach the consideration of the problem, as to how 

 the germ-cells get into the embryo, and, as to the majority, how they 

 reach the so-called "germinal ridge", or, as here suggested, the 

 germinal nidus. 



In taking up this, it also becomes necessary to consider the large 

 yolk-laden cells, termed by Rückert "megaspheres" ('87, p. 98). 



In the first place, it may be well to point out, that the present 

 writing concerns itself with these cells in the skate, a form, in which 

 they have not been described by any previous author. 



Rückert's detailed descriptions apparently refer exclusively to 

 Torjjedo. Although there is no doubt in my mind as to the general 

 application of my finds in the skate to Torpedo also, the possibility 

 of difterences in detail must not be lost sight of. 



In his earlier writings on these cells Rückert was disposed to 

 assign to them a limited rôle in the formation of the blood. In his 

 most recent memoir he guardedly hints at a possible connection with 

 the merocytes; and thus he suggests a genetic relationship to super- 

 numerary spermatozoa ('99, p. 677). 



In citing Rückert's statements concerning them, one must care- 

 fully distinguish between his description of the megaspheres and his 



