192 EINGSLEY AND CONN" 



accompanies the formation of the polar glohnle in the Invertebrates. The star was always 

 •single, nothing comparable to the " Kern-platte " was seen, 1 and in my egg the elongate, 

 globules, arranged in the direction of their longer axes, marked the exact centre of the 

 aster. Though watched for a considerable time no further changes were witnessed, and as 

 the egg was not fertilized no segmentation could be expected. No other eggs of so 

 early a stage were obtained. 



II. Segmentation. 



But two eggs were obtained by skimming before segmentation had commenced, the 

 larger portion having the blastoderm well segmented indicating a development of from four 

 to six hours. In one of these eggs which I found (fig. 4) the protoplasm was collected 

 around one pole of the egg, imparting to it a very pale yellowish tinge and gradually 

 fading out so that at about a third of the distance around the egg it was invisible. In 

 this yellowish protoplasm the germinative vescicle or nucleus was visible and in these a 

 single nucleolus. The egg measured .0375 in., the nucleus .0037 in., and the nucleolus 

 .00055 in. Soon several strongly refractive bodies appeared in the nucleus, similar in appear- 

 ance to, but smaller than the nucleolus. An unfortunate pressure of the cover glass then 

 killed this egg, preventing any further observations upon it. 



Mr. Conn however found a single egg of the same species just as the first segmentation 

 furrow was appearing. He describes the egg as essentially similar to the one which I had, 

 the protoplasm extending down over the yolk in a similar manner. The nucleus, however, 

 was not visible. The segmentation furrow made its appearance at the centre of the sur- 

 face of the protoplasm and gradually progressed outward and downward until the germinal 

 portion of the disc was divided into two blastomeres. During the later stages of this seg- 

 mentation the line of demarcation between the protoplasm and deutoplasm became more 

 distinct, and at the close of the segmentation the protoplasm is gathered up at one pole of 

 the egg as a thick two-celled cushion, as shown in figs. 12 and 13. These changes occupied 

 about a quarter of an hour. 



We made more detailed observations upon the first segmentation of the eggs of Merlu- 

 cius, but as Mr. Van Vleck is intending to publish on the development of this form we do 

 not here relate our results, simply saying that they fully agreed with the description above. 

 This segmentation we regard as the first segmentation of the egg. That of separation of 

 protoplasm and deutoplasm cannot be considered as segmentation, since it is one of the 

 features of the maturation of the egg and is accomplished before impregnation. 



It is to be noticed that in all the eggs which we studied all of the segmentation furrows, 

 including the first, pass completely through the germinal area and in all the segmentation 

 of the protoplasm of the egg is complete. Similar results were noticed by Van Beneden 

 in the egg of an unknown Teleost, and by Haeckel in the egg of ? Motella. On the other 

 hand CEllacher, Strieker ( Truttafario), Van Bambeke (Leuciscus), and Carl Vogt (Coregonus) 

 describe the segmentation planes as at first passing only part way through the germinal 

 disc. 



Returning to our original egg ; from the stage with four blastomeres many observations 

 were made and all features of segmentation were verified and reverified by both of us- 



1 See preceding note. 



