PROCESS OF FERTILIZATION IN THE CRAB 149 
testis to the base of the last thoracic leg. It is extensively con- 
voluted so as to form two large masses, one lateral to the pos- 
terior part of the testis and the other beneath the posterior part 
of the heart. The deferent duct is lined with a layer of columnar 
epithelium which secretes the substance that forms the walls of 
the spermatophores. 
Methods 
Pieces of the testis, obtained by cutting across the organ, were 
fixed in Worcester’s fluid. This is a saturated solution of subli- 
mate in 10 per cent formalin. Other fixing fluids were used but 
did not give as satisfactory results. The sections were cut 74 
to 10 » thick. The stains used were thionin and eosin, safranin 
and Lichtgriin, iron-hematoxylin, and Delafield’s hematoxylin. 
The testicular tubules 
The walls of the tubules of the testis are thin and contain 
flattened nuclei. Figures 1, 2, 3 and 4 are drawings of trans- 
verse sections-of the tubules and show different stages in the 
development of the seminal elements. In figure 4 the tubule is 
seen to be made up of three regions: The smallest one which 
borders the more sharply curved side at the bottom of the draw- 
ing contains mature spermatozoa. Next to this, and filling the 
central region, is a space filled with spermatozoa nearly mature. 
The third region, which forms the crescent shaped portion on 
the upper side, contains spermatocytes in the early prophase of 
the first maturation division. ‘There are more or less definite 
layers of epithelial cells between the different regions of the tubule. 
The outer wall and sometimes these inner partitions which border 
the regions containing mature spermatozoa, become thick and 
columnar in structure (figs. 3 and 4). 
Not only do the seminal elements in these separate parallel 
cavities of the tubule differ in the stages of their development 
but in the same cavity the elements at one end of the tubule 
