THE REPRODUCTIVE CYCLE OF SPHAERIUM SIMILE

1. Reproduction occurs throughout the year in S. simile although definite variations can be observed in different reproductive activities at different times. 2. Gametogenesis and mature gametes are visible to some extent during the fall, winter and early spring (particularly in specimens less than 12 mm long) but the production of gametes appears to be most intense in all adults, regardless of size, in the late spring and summer (especially June and July). 3. Fertilization seems to be most active during the summer, although parents with young resulting from very recent fertilizations can be found throughout the year. 4. Embryos in one or more stages of development are present in the great majority of individuals over 10 mm in length at all times. 5. The birth rate is highest during the winter and summer months. There is a gradual decline in the number of births throughout the spring and fall. During these seasons, however, the embryos inside the parent continue their growth and development; the size of the largest embryos in the adults continues to increase in preparation for the next major period of birth.