108 Dr. M. Schultze on the Development 



at tills period, wliich were here scarcely six inches apart^ a pyri- 

 form gelatinous mass about half an inch long and of a fine rose 

 colour. On examining them more closely, I found that each of 

 them was fastened into the sand by a gelatinous stem of about 

 two inches long, and that the red colour was caused by an 

 aggregation of red granules in the interior of the greenish-yel- 

 low jelly. These are the eggs of Arenicola, of which from 300 

 to 400 are enclosed in the gelatinous mucus (PL II. fig. 1). 



Fi-om microscopic examination of some of them, it appeared 

 that the yelks lay close together in the gelatinous mass, only 

 enclosed in an extremely delicate vitelline membrane, something 

 like those of Nemertes in their pyriform vesicles ; and as I found 

 no traces of the commencement of segmentation, I concluded 

 that the eggs were only just deposited. 



Unfortunately I was unable to trace their development on the 

 spot, and only recommenced my observations nine days after- 

 wards on the egg-masses which I took with me to Greifswald. 

 I then found that the process of segmentation was completed in 

 most cases, and that the oval embryos had acquired a fringe of 

 extremely fine cilia, in the form of a broad band, near what I 

 afterwards ascertained to be the anterior extremity (fig. 3). 

 Other eggs, which were rather backward in their development, 

 although they certainly gave no satisfactory clue to the course 

 of the process of segmentation, showed at all events that this 

 was complete, and that the vitelline membrane had taken part 

 in it so far as to furnish envelopes for the globules of segmenta- 

 tion, and consequently gave off the materials for the walls of the 

 embryonal cells. The embryos could therefore have been enve- 

 loped in no other capsule, but lay quite free in the semifluid 

 jelly, in which they began to move about slowly after the deve- 

 lopment of the cilia. The animals soon became rather more 

 elongated (fig. 3), and with this change of form new circles of 

 cilia made their appearance (fig. 4), one close before and a second 

 close behind the first ciliary band, and a third at the hinder 

 extremity of the body. All three of these are very narrow, and 

 consist only of a few series of very fine cilia, which can only be 

 seen with a high magnifying power, and never exhibit the rota- 

 tory motion which is often so remarkable in the free-swimming 

 Annelidan larvae. At the same time two dark-red eye- spots 

 made their appearance in the neighbourhood of the first circle 

 of cilia. This was the condition of the embryos on the twelfth 

 day. 



The length of the animal now gradually increases, whilst the 

 circles of cilia undergo no change in number or form. On the 

 other hand, distinct annular constrictions make their appearance 

 in the middle of the body, the first close behind the last circle of 



