1916.] NATURAL SCIENCES OF PHILADELPHIA. 23 



spore. Eventually the chromatin of'these elements collects into a 

 number of small aggregates which arrange themselves around the 

 periphery of the parasite and transform themselves into what are 

 evidently the microgametes. It may be assumed that the evolution 

 of the male element, or niicrogametocyte, proceeds in an orderly 

 manner, and hence it should be possible to obtain an orderly series from 

 some such stage as that of fig. 31 (Plate II) to that of fig. 75 (Plate V). 

 It is not, however, possible to give all of the steps of this evolution. The 

 parasites are themselves small, ranging around 8." in diameter and in 

 consequence the details of their structure require the highest powers 

 of the microscope. There is not a great deal of staining material 

 within them, and the picture is confused by the fact that they lie 

 embedded within the cells of the mouse in sectioned material. It is 

 believed that in order to work out this evolution with precision it 

 would be necessary to develop a technique which would permit of 

 obtaining the parasites isolated, an end which could be gained either 

 by cultural methods or by devising some means of getting the para- 

 sites out of the cells in which they had developed. The few attempts 

 which have been'made along these lines have as yet not met with any 

 success. It is therefore to be understood that the details of the 

 evolution of the niicrogametocyte as here set forth are presented 

 with some reserve. 



Taking up now this development of the male from the stage found 

 in the 5- and 6-hour mice to that found at the end of 18 hours, the 

 earlier phases of it are illustrated by figs. 40 to 53 (Plate III). As it 

 happens, most of these are from mice 106 and 120, both of which 

 gave especially favorable material. What is seen here, however, is 

 confirmed by the findings in other mice of the same periods. 



Evidently what is found in the 2- to 6-hour mice will represent 

 conditions earlier than those found in mice killed 9 hours or more 

 after feeding, and in these former the nuclear net is coarse and has a 

 low affinity for chromatin stains (see figures of these stages). It is 

 a matter of common knowledge that the chemical nature of chromatin 

 varies with the physiological condition of the nucleus and that this is 

 manifested by a varying staining reaction. Thus, in the so-called 

 resting nuclei the chromatin has a relatively low percentage of 

 nucleic acid, and this is indicated by a relatively low affinity for 

 chromatin stains. On the other hand, as the nucleus prepares to 

 divide, the percentage of nucleic acid increases, and as this takes 

 place the chromatin displays a greater and greater affinity for chroma- 

 tin stains. The percentage of nucleic acid is greatest at the time 



