No. I ] GERM-LAYERS IM CLEPSINE. 133 



2 . Observations, 



The results of my study on Clepsine parasita are supple- 

 mentary to those obtained on C. marginata (No. i, pp. 57~58» 

 66-72) and C. complanata. For the sake of clearness as well 

 as completeness, I have decided to give both the earlier and 

 the later observations a place in the present paper. The exist- 

 ence of free nuclei in the surface of the three entoblasts, a, b, c, 

 first pointed out in my paper on Clepsine, has been confirmed 

 by Bergh and Nusbaum. The early history of these nuclei is 

 given in the following citation : — 



" About the time the germ-bands begin to form, a number of 

 free nuclei appear in the surface of the entodermal blastomeres, 

 a, b, c. These nuclei are very distinct in the egg of C. com- 

 planata, and it is remarkable that they have so long escaped 

 observation. They appear like dark spots in the opaque yolk, 

 just as the nuclei of the neuroblasts or of the blastodisc. They 

 are oval, oblong, or biscuit-shaped, and measure .02 to .05 mm. 

 At the time of appearance they number three to four in each 

 blastomere, two or three of which occupy the position seen in 

 the figure (No. i. Fig. 37), while the others are near the lower 

 pole. They are encircled by white rings, such as are generally 

 seen around the nuclei of the neuroblasts. The substance of 

 these rings is the same as that of the white borders of the rings 

 and ring-discs. 



" I have seen these nuclei pass through the successive forms 

 of a dividing amphiaster. They multiply rapidly, and, in the 

 stage of Fig. 38, are scattered over the whole outer surface of 

 the blastomeres. In the following stages they can also be seen 

 on the upper faces of a, <:, and b, through the thin ectoder- 

 mal layer. By the time the germ-bands are fully united they 

 are very numerous, and much smaller than at first. 



"Whence come these nuclei? In the stage of Fig. 35 they 

 are not to be seen. A horizontal section of this stage (Fig. 

 80) shows that each blastomere possesses a single nucleus. 

 The nucleoplasm has a somewhat stellate form. The rays vary 

 in length, sometimes reaching to the irregular circular outhne 

 of the nucleus. The same condition has been described in 

 Nephelis by Biitschli. Fig. 61 represents one of these nuclei 

 in a little earlier phase. The nuclei now lie nearer the inner 



