137 



to produce irregularities in the early phases. This irregularity however 

 soon disappears, so that individual eggs have their yolk nearly uni- 

 formly divided (Fig. 3). Nucleus division arises by karyokinesis, 

 periods of rest alternating with periods of activity. 



Irregularities of segmentation are very numerous. One often 

 finds eggs composed of sereval hundred segments , some very small, 



Fig. 3. 



Fig. 4. 



EA' 



Fig. 3. Egg in which yolk segmentation has become nearly regular : about 

 130 yolk segments : clotted limes show the uncompleted cleavage of the yolk in 

 many of the segments. 



Fig. 4. Keel-stage of egg. The wedge-shaped mass of cells (Ä") forming the 

 keel only is represented. In the midst of it is a conspicuous pit, and behind the keel 

 a train of cells (YC) extends into the yolk below the surface. In front of the keel is 

 the embryonic area (unrepresented), consisting of a single layer of rapidly dividing 

 cells. K = Keel. E A = embryonic area. YC = Yolk cells. 



others very large, and of various intermediate sizes. Again, eggs other- 

 wise regularly segmented, may contain a large superficial mass of un- 

 segmented yolk. Then one meets with eggs with yolk quite unseg- 

 mented, with the exception of 2 — G small segments on one part of the 

 surface. 



The segmentation stages occupy about three days under the con- 

 ditions shown in Table II. By the end of the 4th day the invagina- 

 tion stage is reached. This is followed by the keel-stage (Fig. 4.), 

 which lasts about 4 days. By the beginning of the 10th day the nau- 

 plius appendages begin to bud forth, — - first the 1st pair of antennae 

 and mandibles — and a little later the 2d pair of antennae. On the 

 27 th to 30 th day eye pigment can be detected at the surface. 



(Schluß folgt.) 



