Royal Microscopical Society. 199 



called rhombic. We observe further that where the groove is deepest 

 a cord stretches from the embryonal prominence on both sides to- 

 wards the centre of the blastoderm, where the cords of opposite sides 

 meet, forming a ring which completely surrounds the cephalic extre- 

 mity. This ring, which I shall name the secondary elevation, is 

 somewhat thinner than the peripheral elevation, and at the time 

 when I first saw it, it was so large, that its periphery, turned from 

 the embryonal prominence, nearly reached the centre of the blas- 

 toderm. 



In the immediately subsequent stages, until the period when 

 the blastoderm has further grown round half the yolk, during 

 which time the embryonal prominence has apparently become 

 elongated, the circles increase in size, both the circle enclosed by 

 the secondary elevation as well as that enclosed by the peripheral 

 elevation ; but both these elevations decrease in thickness. 



From the stage when the peripheral elevation corresponds to 

 the greatest circumference of the e^g, the circle enclosed by the 

 secondary elevation increases, whilst of course that of the peri- 

 pheral elevation decreases, because the blastoderm now begins to 

 grow round the other half of the yolk. 



About the twentieth or twenty-first day the blastoderm has 

 grown round the yolk so far, that a portion only of the yolk, no 

 larger than the head of a pin, is exposed ; the embryonal j)romi- 

 nence is very long and thin. 



Of a dorsal groove nothing more is to be seen. The peripheral 

 elevation, now confined to a small ring, is just to be seen as such ; 

 the secondary elevation also, which now forms the equator of the 

 egg, is just perceptible. Soon after (half a day to one day), the last 

 indication of the peripheral elevation, as well as of the secondary 

 elevation, disappears, and the last remains of the opening lying 

 behind the tail of the embryo, on which the yolk was exposed, have 

 disappeared. The blastoderm has become closed behind the tail, 

 and has therefore grown compleiehj round the yolh. We cannot 

 therefore speak of the existence of an opening which should 

 become the anus (Busconi and SlricJcer). 



If we make a thin section through the embryonal prominence 

 of an egg seventeen or eighteen days old, which embryonal promi- 

 nence has been hardened in very dilute chromic acid, we find 

 that the embryonal prominence consists of the following layers : 

 an upper layer corresponding to the corneous layer (Hornblatt) ; 

 and then under this a nervous layer (Nervenblatt), consisting of 

 several layers. Under this there follow two layers more (motorisch- 

 germinatives Blatt and Darmdriisenblatt), each of which consists 

 again of two layers of larger cells. The nervous layer raises the 



