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1. The work presented in this paper has proved the presence of size dimorphism in the adult spermatozoa of Anasa tristis. Measurements of the length of the chromatic rod of several hundred spermatozoa from each testis, plotted as a frequency curve, have demonstrated two modes, one between 27.54µ and 28.08µ, and the other between 30.24µ and 30.78µ, and the data offer adequate support for the conclusion that length dimorphism exists.2. This dimorphism in length of adult spermatozoa probably bears a fundamental relation to the dimorphism in chromosome number revealed by spermatogenesis studies.

The spermatogenesis of Leptocoris hcematoloma (family Coreidoe) very closely resembles that of Anasa tristis, as described by Paulmier. During the past few years it has been used extensively here in the course on cytology to demonstrate the behavior of the X-chromosome. As a matter of record, it seems worth while to give a very brief account of the spermatocytic divisions. Furthermore, the material is very fine for the study of tetrad formation, and it is hoped later to publish an account of this process. The material on which these observations were made was collected in November and December, I914, on the plant Cardiospermum halicacabum, the balloon vine which is very common in this vicinity. It may be of interest, however, to know that this is the only plant on which we have found this bug. The testes, which are large yellow pear-shaped bodies located at the base of the third pair of walking legs were dissected out in Ringer's solution and fixed immediately in Bouin's fluid. They were stained with iron haematoxylin and counterstained with eosin and light-green. Other fixing agents were used, but this proved to be the best. The material is excellent for the study of spermatogenesis, as the chromosomes are not numerous, and vary greatly in size. It is possible to follow accurately the courses of the smallest, largest and accessory chromosomes throughout their entire history. The spermatogonial complex of Leptocoris hcematoloma consists of thirteen chromosomes (Figs. I and 2). These vary in size, but can be classified in three groups. The members of two pairs 1Contributions from the Zoological Laboratory of the University of Texas, No. I38. 316