No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 439 



since the yolk balls increase in size at the beginning of the 

 metaphasis, though there appears to be no increase in their 

 own ground substance. These unstaining globules are at first 

 localized at different points in the yolk ball ; and it would seem 

 probable that their substance later mixes itself with the ground 

 substance of the yolk ball, since this supposition would account 

 for the lessening intensity of the stain of the yolk ball during 

 the metaphases. It would appear less probable that these 

 globules are metabolic products of the true substance of the 

 ball ; however, we have too few facts to enable us to deter- 

 mine which of these is the correct view. 



Certain curious structures found in the cytoplasm of an 

 immature worm fixed with Lang's fluid (aqueous corrosive 

 sublimate solution, NaCl, acetic acid) may be mentioned here. 

 In the cytoplasm of a number of ova, in none of which any 

 yolk was present, I found a few small, ring-shaped bodies, 

 which stained with haematoxylin much more intensely than 

 the surrounding cytoplasm {Yk. Bl.f Fig. 233). Each con- 

 sisted of a ring composed of a dense, homogeneous substance, 

 the inner surface of the ring being smooth, but the outer irregu- 

 larly jagged, this whole ring (as it appears on a section) enclos- 

 ing an unstaining vacuole or globule. In reality these bodies 

 are spheres, but my description applies to sections of them. 

 These structures vary considerably in size, and sometimes are 

 not spherical but oval, the larger ones usually staining more 

 deeply than the smaller ones. I found them only in some of 

 the ova of this one individual, and nothing of the kind was to 

 be seen in the ova of about twenty other individuals sectioned, 

 which had been variously preserved in picric, osmic, and chromic 

 acids, in simple aqueous solution of corrosive sublimate, and in 

 the fluids of Hermann and Flemming. Accordingly, they must 

 be regarded as artefacts, produced by the action of the acetic 

 acid, which I have long since found to be a very unreliable fixa- 

 tive for the cytoplasmic elements of the nemerteans. It is 

 most probable that they are young yolk balls, to which the 

 acetic acid has given an abnormal appearance. Or might they 

 represent multiple asters, such as have been recently described 

 by Mead in Chaetopteriis f 



