520 
The Ohio Naturalist, 
[Vol. VI, No. 7, 
In carrying forward the work I have been greatly aided by 
two men who have “seen me through” it, and checked up and 
verified my observations as the work proceeded. They are 
Professor Francis L. Landacre of the department of Zoology 
and Professor John H. Schaffner of the department of Botany, of 
the Ohio State University. To both I wish to extend my heartiest 
thanks. The slides on which the work was done belong to 
Professor Landacre and have been used by the students in the 
Department of Zoology, studying principally the later stages, 
for several years. They are cut from a female of the variety 
bivalens and are arranged in series lettered backward from A 
which contains two-and four-celled embryos, to M in which are 
found the early stages but little removed from the resting nu- 
clei of the oogonia. All of the nuclei drawn for the plate of this 
jjaper except fig. 12, were found in series M and L. 
The difficulties in Ascaris are, I am inclined to believe of two 
sorts: first the problem of staining and second, the minuteness 
of the critical stages. The slides are stained with Heidenhain’s 
Iron Alum Heamatoxylon. To find material in which the nuclei 
were properly stained it was necessary to select extremely faint 
slides in which all of the stain had been drawn from the cyto- 
plasm and spindle leaving the nuclei standing out clearly by 
themselves. Even then the spirems are often so closely knotted 
together and deeply stained as to make resoulution impossible.^ 
In the matter of magnification I find that the 1-12 objectives 
which have beeir mostly used are far inferior for this work to the 
1-16 which was used with a variety of oculars. Of these the 1-2 
inch was the most saitsfactory. Lower oculars do not cut the 
plane of focus sharp enough to enable one to follow out the 
spirems. 
The variety bivalens is a more favorable object for study than 
the variety univalens, for as Tretjakof remarks, the development 
of the two tetrads usually proceeds unequally so that one is 
often found in a much more advanced stage than the other. 
This frequently enables one to understand figures which without 
such aid would be difficlut of interpretation. In fig. 9, for ex- 
ample, one tetrad is clearly differentiated while the loop that 
will form the second is still much twisted. This might be inter- 
preted in a number of ways were it not for its fellow which re- 
quires us to homologize the loop to a tetrad. 
The process of tertad formation in Ascaris is in close agree- 
ment with that more recently described in ‘‘many Arthropods, 
Amphibia” (Montgomery (6) and the higher plants, though the 
appearances are quite different in the different cases. In all 
these there is a precocious longitudinal division of the spirem, 
which through subsequent contraction becomes more or less in- 
visible. Contemporary with this or following it is a conjugation 
