256 MEAD. [Vol. XIII. 



have peculiar nucleoli (Fig. 59). I have paid less attention to 

 the glands on the ventral side. At a stage like that of Fig. 64 

 and text Fig. X, the gland cells present a new appearance. The 

 outer end of each cell (the end of each duct), becomes filled 

 with a substance which stains very deeply with methyl-green, 

 hasmatoxylin, etc., and a few hours later this substance fills 

 the duct and the upper part of the body of each of the gland 

 cells (text Figs. XI-XVIII). Meanwhile two other pairs of 

 gland cells appear in the head segment just behind the proto- 

 troch. They are bilaterally placed; one pair close together on 

 the ventral side just back of the mouth, the other pair also 

 close together on the dorsal side. 



When the larvae from twenty-four to thirty-five hours old are 

 killed in Perenyi's fluid and stained with Biondi Ehrlich, the 

 numerous glands are brought out in brilliant contrast to the 

 other tissues, for the latter are light red, while the glands are 

 an intense green. The body of each gland becomes greatly 

 distended. In larvae five days old mucous glands appear also in 

 the paratrochal region. All the glands, at least in the head 

 region, are unicellular and ectodermal. 



Nervous system. — The two eye spots which are formed at 

 the beginning of the second day persist until at least the 

 eleventh day, — long after the disappearance of the ciliated 

 organs. They are simple structures, consisting of an outer 

 brown pigment, a clear lens, and apparently an optic 

 nerve. 



The cluster of columnar cells immediately under the apical 

 tuft represents, I presume, an apical sense organ (Fig. 64). 

 That the brain arises from the " first group of micromeres," i.e., 

 from the four upper cells of the 8-cell stage, — the "encephalo- 

 blasts " of von Wistinghausen,^ — there can be no doubt; but 

 so do many other organs, for example, the mucous glands, and 

 the greater part of the prototroch. In comparatively early 

 stages the fibrous portion of the brain can be made out directly 

 under the apical pole. I do not know from what cells the 

 brain arises, and, while it may come from the cross cells, as 



^ Wistinghausen, C. v.: Untersuchungen liber die Entwicklung von Nereis 

 Dummerillii. Mitih. a. d. Zool. Stat, zu Neapel., Bd. lo, 1S91. 



