Emhryology of the Uiver-Lamprey . 31 



more precise investigation in the realm of embryology than 

 was possible in former years. Thus it may be readily under- 

 stood that, thanks to these new scientific processes, many 

 deficiencies which existed also in our knowledge of the 

 developmental phenomena in the Lamprey are supplied by 

 numerous fresh investigations. The new facts bring with 

 them new questions, which have a special interest for compa- 

 rative embryology. As the publication in their entirety of 

 my investigations upon the development of the Lamprey is 

 not immediately possible, since the exceedingly abundant 

 material from all stages of development must be arranged in 

 proper order, and since also the figures require much time, I 

 have determined to give a short provisional communication, 

 which is at the same time intended to complete the investi- 

 gations which I made upon this subject nearly twenty years 

 ago. 



In the ova of lamprey larv^, which are from 70 to 90 

 millim. in length, the germinal vesicle is in many cases already 

 excentric in position. At this period of development, when 

 the contents of the ovum are in a semifluid state, the germinal 

 vesicle may alter its position. I have had occasion to observe 

 in a preparation three young ova in which the germinal 

 vesicle lay between the yolk and the egg-membrane. 



The Graafian follicles are clothed with endothelial cells. 

 At the region where the pointed angles of the cells are in 

 contact with one another, which is usually at the upper pole 

 of the ovum, dark spots are to be seen after treatment with 

 nitrate of silver ; these may be regarded as entrances into the 

 lymph cavities. 



The blood-vessels enter the Graafian follicle at its pointed 

 end, at which spot the active pole of the ovum also lies within 

 the follicular membrane. It is frequently to be observed that 

 the tip of the ovum does not quite touch that of the follicular 

 membrane, while everywhere else the latter is in close con- 

 tact with the ovum. 



In all ova of lampreys which were ready to spawn when 

 they were removed from the ovaries I have observed the 

 germinal vesicle with the greatest distinctness in sections. 

 The germinal spot, however, was not present. On the other 

 hand, in very many ova which were squeezed out of the 

 female for the purpose of artificial fertilization the vesicle 

 could not be detected. In very few cases did it lie near the 

 active pole of the ovum as a small flattened disk of the vitel- 

 line membrane. It is hardly open to doubt that in the cases 

 in which the ovular nucleus is not visible its contents have 

 mingled with the elements of the yolk, for all the ova were 



