1102 The American Naturalist. [November, 
order of division, which after the first two divisions loses all appearance 
of regularity. On account of these circumstances the segmenting ova 
vary widely in appearance, and the process of cleavage thus acquires 
"that apparent irregularity which other observers have found so per- 
plexing. It is now well known, however, that the segmenting ova of 
various other animals (e.g., Mollusca, Coelenterata) are likewise subject 
to considerable variation, which in some cases at any rate is due simply 
to temporary acceleration or retardation in the divisions of individual 
cells (No. 53), and probably does not affect the essential character or 
the end-result of the cleavage. 
Preparation of the Embryos of Lumbricus.*—' The demon- 
stration of the teloblasts of the germ-bands may be effected in the fol- 
lowing manner: Take embryos from .5 to .8 mm. long, place them in 
fresh filtered lemon juice 5 minutes, and then 20 minutes in 1% gold . 
chloride ; and then, for reduction, in a mixture of one part formic acid 
and four parts water (in daylight). After one or two hours the embryos 
become reddened and quite soft. They are then to be placed on a slide, 
the dorsal body-wall torn off, and the isolated ventral wall so placed 
that its outer surface faces upward. Examined in water, the teloblasts 
and cell-rows are seen with great distinctness. 
For finer purposes the foregoing method is not to be used. It is better 
to use Flemming’s chrom-osmiuo-acetic acid. The embryos remain in 
this a few minutes, and are then removed to a 14% solution of platinum 
chloride for twice or three times as long. After such treatment sur- 
face preparations are best examined in glycerine. Preparations for 
sections are stained in aqueous hzemotoxylin. 
For demonstrating the median ventral plexus of nerve cells, the 
treatment with lemon juice and gold chloride is followed, except that 
the reduction is effected in very dilute acetic instead of formic acid 
(in daylight). After two days (in winter) the embryos are violet 
colored, and may then be hardened in alcohol (in the dark), and pre- 
pared for the microtome in the usual way. In quite young embryos, 
the epidermis, neural plates, and muscle plates appear clear, and only 
the nerve cells are stained dark violet. 
* R.S, Bergh. Zeitschr. f. wiss. Zool., L., 3, Sept. 1890, pp. 474-5 and 484. 
