92 
ZOOLOGY: ZELENY AND FAUST 
The head-lengths of spermatozoa from fifteen species of animals were 
measured. The number of measurements for a single determination 
ranged from 322 to 1008 with an average of 523, including in each case 
only the spermatozoa from a single testis. A considerable variation 
in length was present and when the frequency distributions were plotted 
the resultant curves were found to be distinctly bimodal in fourteen 
of the fifteen species. One of these curves is shown in the accompany- 
ing figure. The complete data are summarized in a table. The infer- 
ence is drawn that there are two groups as regards size among the func- 
tional spermatozoa of these species, the group with the larger individuals 
in each case consisting of those which the studies in spermatogenesis 
have shown to have the larger chromosomal volumes. 
The species for which these determinations have been made belong 
to several animal groups: 
Diptera: Musca domestica, three determinations. 
Heteroptera: Lygaeus palmii, two determinations. 
Alydus pilosulus, two determinations. 
Anasa tristis, ten determinations. 
Coleoptera: Trirhabda tomentosa, one determination. 
Phytonomus punctatus, two determinations. 
Orthoptera: Melanoplus femur-rubrum, one determination. 
Melanoplus differentialis, three determinations. 
Gryllus abbreviatus, one determination. 
Odonata: Aeshna canadensis, one determination. 
Amphibia: Rana pipiens, one determination. 
Reptilia: Pseudemys troosti, two determinations. 
Mammalia: Ovis aries, one determination. 
Bos taurus, one determination. 
Canis familiaris, one determination. 
In all but one of these species two size-groups were recognized. The 
exception is the one determination of Gryllus abbreviatus. Chromosomal 
dimorphism has been described for all of the groups except the Am- 
phibia, in most of the cases for the particular species here studied. 
A further proof of the close relation between the chromosomal di- 
morphism of the spermatids and the dimorphism in size of the adult 
spermatozoa was sought in a determination of the volume of chromo- 
somal material in each of the two kinds of spermatids. From the vol- 
umes obtained the expected ratio between the head-lengths of the result- 
ant spermatozoa was calculated under the assumption that the volume 
of the heads is directly proportional to the amount of the chromatin 
received and that the shape is the same in the different sizes. 
