The germ-cells. 643 



ing germ-cells have many representatives. In the cranial region there 

 is a single one, lying over the mid-brain beneath the skin. It is of 

 the large variety, and 6 sections of V200 ™"^ go through it. Further 

 back there are many others, especially in the pericardial region. A 

 section through a group of such is shown in Fig 51. 



It is characteristic of many of the cells of these groups in this 

 embryo, and in others also, that they hang together, i. e., that they 

 are incompletely separated. Moreover, many of the larger ones are 

 multinucleated, and careful examination under the Zeiss 2 mm apo- 

 chromatic lens has convinced me, that the nuclei have a definite con- 

 centric arrangement, taking the form somewhat of a spiral. Further 

 consideration may be deferred to the general part of the paper. It 

 has already been described by Rückekt in his "megaspheres". 



The largest of the aberrant germ-cells of this embryo resemble 

 in size that shown in Fig. 36. Others of them are smaller, and 

 more like that of Fig. 18, and the remainder are of the average 

 size of normally placed germ-cells. That is to say, the wandering 

 germ-cells represent the products of at least three ditïerent cell- 

 generations. 



Though often found in certain germinal layers, they are not 

 there as members of such. They may be in a layer, but they are 

 not of it. Very often they are, as in other cases, between the layers, 

 or applied to one without being really in it, or, lastly, they may be 

 encapsuled. 



The final point of importance is, that in the actual genital region 

 of this embryo the germ-cells are represented by 1) those normally 

 placed, 2) some in the gut-epithelium, and 3) such cells as were met 

 with in embryo No. 454 (32 mm). 



Here in the permanent genital region there is a complete absence 

 of any between splanchnopleure and hypoblast, wandering upwards into 

 the embryo. This process, so characteristic of embryos of 6 to 11 mm, 

 has now ceased. 



VI. The eerm-Cells of EmI)ryos of 31—33 mm. 



Embryos of this period present the following external characters. 

 All the gill-clefts are open to the exterior, the spiracle is still elong- 

 ated, and there are short external gills on the three or four anterior 

 branchial arches. The paired fins are small, and there are as yet no 

 traces of the dorsal unpaired fins. The lateral line does not extend 

 beyond the gill-region. The choroid fissure of the eye is still open. 



