viz. early last December, the genital organ invariably laid transverse to the longitudinal axis, and occupied a very large portion of the bulk of the posterior end of the body. Most frequently it had a U-shaped form (fig. 3, n), and embraced the contractile vesicle with its two limbs. It was then of a yellowish brown color and perfectly homogeneous. Occasionally it was observed to be divided into three or four masses, which extended toward the region encompassed by the posterior annular furrow. While in the U-shaped form the whole semi-opaque mass was enclosed in a transparent envelope (ne). Oftentimes there was to be seen immediately over and close to the dorsal region of the nucleus and directly in the plane of the axis of the body, a minute, clear, vesicular corpuscle (fig. 3, t), which seemed to have the character of a "nucleolus" or as is now becoming the belief, since the investigations of Balbiani and Claparéde - a testicle.

Reproduction from the egg has not been observed, but transverse division occurred in a number of instances. In the latter case it agrees, in the process, with what Allman, loc. cit., has described, excepting that the resultants (fig. 6, I., II.; fig. 7) are quite different in their proportions from the adults (fig. 1, 2, 3). At the moment of separation the young offshoot (fig. 7) is about two thirds the size of the adult, and is almost as broad as long, and bulges strongly on the ventral side (V), in front of the mouth (m). It has a very flat anterior end, and the pseudo-cuirass (pc) of this part is represented by an inconspicuous unguiform body. The anterior transverse furrow, on account of its narrowness, hardly attracts attention, except along its ventral edge (af), where it is rendered conspicuous by the strong projection of the unguiform cuirass. As in the adult, it is broadest ventrally, but, growing shallower, thins out (af1), going dorsally, to almost nothing. The relations and structure of the various organs, cilia, &c. are the same as in the full-grown individuals; but with progressing growth the proportions of the diverse regions of the body change insensibly, as may be seen by comparing figures 7, 4, and 1, which are respectively representatives of the youngest, middle-aged, and adult individuals.

Description of Figures.

In all the figures the same letters refer to corresponding parts.

A. The anterior end of the body. P. The posterior end.

D. The dorsal side. V. The ventral side. R. The right side.

L. The left side.

af anterior transverse, or annular furrow. af1. dorsal part of af.

pf. posterior transverse, or annular furrow.

mf. median, or longitudinal furrow.

d. depression on the ventral side.

cv. contractile vesicle.

m. mouth. m1. anterior edge of m.

œ. œsophagus.

do. digestive vacuoles.

A. pseudo-flagellum. A1. base of fl.

n. nucleus, or generative organ. ne. envelope of n. This is the reproductive organ, properly speaking, and n is the contents, or reproductive material, the future eggs.

t. nucleolus, or testes.

pc. pseudo-cuirass.

I., II. The two products of self-division. III. The annular constriction which finally separates I. and II.

Figs. 1 to 7. Peridinium Cypripedium, n. sp.

Fig. 1. Profile of an adult, seen from the left side. Mag. 500 diam.

Fig. 2. View of the ventral side of an adult. Mag. 500 diam.

Fig. 3. Posterior view of an adult; the anterior end in the distance. Mag. 500 diam.

Fig. 4. A young individual. Mag. 300 diam.

Fig. 5. An adult gradually dried up. Dorsal view, to show the arrangement of the punctiform ornamentation of the derm. 500 diam.

Fig. 6. The process of self-division, just half an hour before separation. Ventral view. 200 diam.

Fig. 7. Profile of I. fig. 6, just at the moment of separation. 200 diam.

The following memoir by Mr. Francis was presented by Professor Treadwell with these introductory remarks:

About five years ago I called the attention of the Academy to the subject of the strength of cast-iron columns, and presented a paper, which was printed in the Proceedings, containing a short examination of the state of our knowledge upon that subject. It was then thought desirable that a more elaborate examination should be given to it; and a committee was appointed for the purpose. This committee, after two or three consultations, gave over all attention to it, and there the matter has rested, so far as the committee, as a body, were concerned, to this day. One of their members, however, Mr. J. B. Francis of Lowell, whose professional engagements gave him a particular interest in the investigation, finding that nothing would be done by the committee collectively, took up the subject in his own way, and has pursued it at his leisure up to the present time. He has made a most

thorough examination of all the experiments that have been published, or that came within his reach, with the conclusions which have been drawn from them, together with the formulas and rules that have been proposed for practical constructions. Proceeding thus, he has, after a careful and patient examination of the experiments and the reasoning of the several investigations, selected such of the conclusions and formulas as have appeared to him quite trustworthy, and from combining, and, in some cases, modifying these, he has calculated a most elaborate set of tables, by which the architect or practical workman can find a column suited to any structure, and which may be relied upon as safe for all purposes, ordinary, or even extraordinary. I consider the paper thus produced by Mr. Francis as of great value, and believe that it will become a work of the first authority, and of constant reference for the builder.

This paper might, most properly, have been presented to the Academy by Mr. Francis himself, and I think ought to have been thus presented, without my intervention. He has, however, (probably from my having formerly called the attention of the Academy to the subject, and having been chairman of the committee before referred to,) requested me to present the paper for him. I consider myself honored in being thus called upon to communicate a work of such merit to the Academy. Let it be understood, however, that I do not present it as chairman of the committee formerly appointed to examine the subject (this committee have really produced nothing from their charge), but as the sole and private work of Mr. Francis, who alone is entitled to the thanks of the Academy and the community for his most laborious and useful work.

On the Strength of Cast-iron Pillars, with Tables, for the Use of Engineers, Architects, and Builders. By JAMES B. FRANCIS, Civil Engineer.

Until the year 1840 the only rule in common use for computing the strength of cast-iron pillars was that given by Tredgold, in his essay on the strength of cast-iron and other metals.* This rule was not founded on experiments made on pillars, or on sound theoretical

* Practical Essay on the Strength of Cast-iron and other Metals. By Thomas Tredgold, London, 1822, and three subsequent editions.