46 T. H. MORGAN. 



(This is not drawn to the same scale as* XIV.) The bunches on 

 each leg are entirely separated from each other, while in Phox- 

 ichilidium (see Fig. XXIV) the bunches are larger than in the 

 last (but with the eggs individually smaller), and are stuck to 

 both of the ovigerous legs, which are thus bound firmly together 

 by the sticky masses of eggs. 



Before leaving the metamorphosis of Tanystylum, I wish to 

 refer briefly to the development of the ventral ganglia. I had 

 previously shown in Pallene that each ventral ganglion was 

 formed by an invagination of the ectoblast, and I was led to 

 infer a similar formation in Tanystylum, and by inference for all 

 of the Pycnogonids. A study of the metamorphosis of Tany- 

 stylum has verified this beyond all doubt for that form, and I 

 think it will be legitimate to extend this to the whole group. 



The earliest stages of the development of the ventral organs in 

 Tanystylum are shown in Fig. 52, Plate YIII, where the thickened 

 ectoblast pushes in at two points on each side of the mid-ventral 

 line. The nuclei of the cells of the invagination at this stage are 

 scarcely, if at all, larger than those in the rest of the ventral 

 ectoblast. A later stage in the formation of these ventral organs 

 is shown by Fig. 54. It is taken from the third pair of ganglia. In 

 this the cavities of invagination have closed, and the ganglion is 

 now cut off from the ventral ectoblast. There are many 

 ganglion-cells or nuclei forming the ganglion, and the nuclei in 

 the cells bounding the cavities are larger, and often er show karyo- 

 kinetic figures than do the other nuclei of the ganglion. The last 

 stage of development is shown by Fig. 53. Here the central 

 cavity is almost obliterated on the right side, but on the left side 

 the section cuts a little to one side of the central cavity, and only 

 the cells of the wall appear, and two of these are seen in process 

 of karyokinetic division. It is to be noted that the nuclei of the 

 ventral organs at this stage are seen to approximate in size to 

 those nuclei forming the substance of the ganglion, but stain 

 more deeply. If we examine a little later stage, the central cav- 

 ities of the ganglia have disappeared completely, the nuclei are 

 all of the same size, and the only indication of the ventral organs 

 is in the deeper staining of the cluster of nuclei at the spot in 

 each ganglion where the cavity was last seen. Ultimately this 

 difference also disappears. 



