520 The Ohio Naturalist. [Vol. VI, No. 7, 



In carrying forward the work I have been greatlv aided bv 

 two men who have "seen me through" it, and checked up and 

 verified my observations as the work proceeded. Thev are 

 Professor Francis L. Landacre of the department of Zoology 

 and Professor John H. Schaffner of the department of Botanv, 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 

 paper except fig. 12, were found in series M and L. 



The difificulties 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 been 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. Lowxr 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 (O) 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 



