NOTES AND MEMORANDA. 99 
Anatomy of the Arms of the Crinoids,” by P. H. Carpenter; “On 
the Structure of the Retina,” by Dr. J. C. Ewart and Dr. G. Thin. 
This is a most valuable paper, and we regret that it has had to be 
reduced in length to meet certain editorial requirements, for it was 
before its reduction a useful summary—besides the author’s own 
investigations—of the progress that has up to Max Schultze’s time 
been made in this direction of microscopic work. 
Archives de Zoologie Expérimentale et Generale, publiées sous la 
direction de H. de Lacaze-Duthiers. Tome 5. 1876. No. 1.—This 
number is much taken up with a zoological paper which has no 
microscopical interest. Still it has one important communication on 
the development of Mollusks, by Dr. Hermann Fol. This paper, 
which is one of a series, is upon the embryonic and larval develop- 
ment of the Heteropoda, and is admirably illustrated by four well- 
executed and some of them coloured plates. Some of the terms used 
seem to be peculiar in their application. ‘Thus the word lecith, and 
its compounds proto-lecith and deuto-lecith. Of this the author says: 
“ With me the term lecith is synonymous with vitellus; the proto- 
lecith is the nutritive substance which the ovule possesses as it leaves 
the genital gland; the deuto-lecith is the nutritive material that the 
vitellus absorbs only after fecundation and even after division of the 
yelk” (apres le fractionnement). This is a long paper (over 30 pp.), 
and it follows out the development of certain genera of Heteropods 
with much minutiz.—Another paper of considerable value is a review 
of Herr R. Hertwig’s paper, “A Contribution to the History of 
Acineta-forms.’ The author describes at some length a fine species, 
Podophrya gemmipera, which is found in Heligoland on the stems and 
branches of almost all the hydroid polyps of the shore. The paper 
has an especial importance, from the fact that it combats with 
Cienkowski the idea that all the species have a special wall or 
envelope enclosing them. He shows that some of them remain naked 
through their entire life. 
NOTES AND MEMORANDA. 
An Objective of Mr. Spencer’s.—Mr. Spenger is an American 
maker whose glasses from various circumstances are not likely to come 
into the English market. We may therefore quote the following 
passage descriptive of one of his objectives which the editor of the 
‘ Cincinnati Medical News’ (December 1876) has had in his possession : 
—‘ For several weeks we have had in our possession an immersion 
zyth, made by Mr. Spencer, marked 160° angle of aperture. In re- 
solving power, brilliancy, and sharpness of definition, flatness of field, 
and in all the essentials of a pre-eminently fine glass, we have 
certainly never met its superior, and very few its equal. All of the 
most difficult tests yield to it without the slightest difficulty, and pre- 
