192 



the point is very significant, that in the fifth embryo the germinal 

 nidus of each side is as highly developed as in a normal embryo of 

 more than double the size. The embryos were not measured, this 

 being impossible owing to their contortions. 



A point of special interest about them is, that they would appear 

 to have been arrested at a period corresponding to that, in which one 

 so frequently encounters monsters among pig-embryos. In their turn 

 these latter are again interesting, because among them are represen- 

 tatives of almost all, if not all, of the abnormal early human embryos, 

 figured by His. Into the general law, if as is probable such there be, 

 governing such instances of arrested development at like periods in 

 skate, pig, and man, it is not proposed to inquire here. All that need 

 concern us is, that along with other abnormalities in every in- 

 stance a glaring deviation from the normal is observ- 

 able in the behaviour of the germ-cells of the monster 

 skate-emb ryos. This is probably a consequence of the abnormal- 

 ity of the embryo, and not a cause thereof. 



The embryos are numbered nos. 742 — 747. 



R. batis no. 742 exhibits a unilateral deficiency in the actual, not 

 the microscopic, right side of the body. Here the gill -pouches are 

 somewhat arrested, further back the myotomes and segmental duct. 

 On the left side, on the other hand, all these structures are quite 

 normal. As to the germ-cells, whereas they are abundant on the right 

 or arrested side of the body, to the left of the middle line, beyond 

 two free in the body-cavity and a few within the lumen of the gut, 

 there is throughout the entire embryo a complete ab- 

 sence of germ-cells. 



R. batis no. 743 is very like the preceding embryo, and of about 

 the same grade of development. But the abnormalities in the struct- 

 ure of the embryo relate more to the left side of the body. In this 

 case there are plenty of germ-cells on the left side of the middle line, 

 while there are very few on the right. 



R. batis no. 744 is possibly the most remarkable of the series. 

 The embryo is arrested in development at a period but slightly in 

 advance of the preceding two; moreover, it is deficient in the head- 

 region, no part of this in front of the auditory organ being repre- 

 sented, e, g., there are no foundations of eyes or olfactory organs. 



Were proof still lacking of a genetic connection between the so- 

 called megaspheres and the germ-cells, the embryo under review would 

 furnish it. Here the large megaspheres, equivalents of eight, four 



