The Microscope. 233 



sigmoides. As many as eight zooids were noticed in a group, but 

 not a trace of a sui'rounding gelatinous envelope was to be seen. 

 The animals differ from those of O. sessile, and the groups seen 

 were all smaller ; the only real generic difference is the absence of 

 the zoocytium. But the difference is sufficient, and the diagnosis of 

 Gerda needs amending by adding or social to " Animals solitary,'" 

 etc. If the species differs from Sigmoides it may be called Gerda 

 socialis. 



Buffalo, N. Y. 



A NEW OBJECTIVE. 



BY T. J. BURRILL. 



T HAVE recently received direct from Carl Zeiss, of Jena, Ger- 

 -*■ many, one of his new " apochromatic " objectives, together with 

 three oculars of special construction. The order for these was made 

 last summer, for the University of Illinois. 



Arriving, as it did, during the closing days of our scholastic 

 year, I could only give the objective a hasty examination, and from 

 this was obliged to admit to myself, a feeling of disappointment. I 

 used a Bullock '• professional " stand having a tube length of ten 

 inches. This length could be increased by the draw tube, but could 

 not be made less. The objective was ordered for the long tube and 

 has engraved upon it: ''Tubusl, 250 mm." I tried first central light 

 both from the northera sky, which at the time was white with well 

 distributed clouds, and from a lamp with various methods of con- 

 densation. The results were certainly good, but I could not see any 

 improvements over the best work upon the older formulae of Spencer 

 and ToUes, with which I was very familiar, or upon that of Zeiss 

 himself as represented by his well-known one-twelfth and one- 

 eighteenth homogeneous immersion. 



Trying oblique light similar conclusions were reached, except 

 that upon looking at a dry mount of Surirella gemma, turned at 

 right angles to the illuminating beam, the basket-like work between 

 the transverse ribs stood out with conspicuous brilliancy. Of course 

 this was not a high-class test, but the excellency of the picture was 

 worth the record. Putting on a slide of Amphipleura pellucida, 

 mounted by Moeller in monobromide of naphthalin, with lamp-light 

 direct from mirror, the striae were at once resolved and visible 

 enough for recognition by any tyro. This again, however, was no 

 advance over the performance of the older objectives named above. 



