Seasonal Variations in the Interstitial Tissue of the Testis of the Horned Toad (Phrynosoma solare).

Abstract

A histological study has been made of a series of Phrynosoma testes taken at frequent intervals throughout the year, with special reference to the problem of interstitial cell function. If, as thought by some, their function is the control of sex activity then they should show seasonal changes correlated with the breeding period. Although such work has been extensive on other groups, particularly in the amphibia, practically nothing has been done on the reptiles.

Seasonal changes in the interstitial tissue should be expressed quantitatively. In this it is important to differentiate between the volume of tissue and the number of cells since these do not seem to be directly proportional. In expressing volume changes, the actual volume and not relative volume was calculated since the testis as a whole shows seasonal variations in size. Counts of the number of interstitial cells per unit volume were made and from these the relative number of cells for testes of different seasons was calculated.

The results show definite testicular cycles. The total volume of the testis undergoes a marked seasonal change, reaching a maximum during the breeding season. This is an external expression of the spermatogenetic cycle which gives changes in diameter, total length, and volume of the seminiferous tubules. These changes have been measured and recorded quantitatively.

The interstitial cell cycle is definitely correlated with the sperma-togenetic cycle. The size of the interstitial cells and of their nuclei is greatest during the breeding season. Following the period of sex activity a syncytial condition exists in which the cell boundaries are very indistinct or totally lacking. At this time the nuclei are smallest. At no time do these cells revert to a connective-tissue-cell type. The number of interstitial cells decreases as the breeding season advances. The minimum number is reached at a time when the testis is gorged with spermatozoa. There is a marked increase in the number of interstitial cells at the close of the breeding season when all the spermatozoa are extruded. The volume of interstitial tissue is twice as great during the height of sperm production as it is during the period which follows.