PROCESS OF FERTILIZATION IN THE CRAB 165 
Changes in the nuclear cup 
When solutions with a lower osmotic concentration than sea- 
water come in contact with the nuclear or protoplasmic cup it 
becomes thicker and the pseudopodia are withdrawn so that the 
outline of the spermatozoon, viewed from the top or bottom of 
the cup, is circular instead of star-shaped. The disappearance 
of the pseudopodia proceeds by a swelling at the base while the 
outer portion tapers very gradually to an extremely fine point 
(compare fig. 62 with 63 and 65). As the base widens out still 
farther the rays are reduced to a very fine thread, which either 
breaks off or is contracted into the body. When the pseudopodia 
break loose from their attachment the whole spermatozoon is apt 
to move suddenly and then be borne away if there be any cur- 
rents in the containing fluid. This sudden movement probably 
results from some of the pseudopodia breaking loose slightly 
before the others. This rather than the explosion of the capsule 
may be the explanation of the ‘springing of the sperm’ discussed 
by Koltzoff (06). This rounding up of the protoplasmic portion 
of the sperm is apt to be completed before any change takes 
place in the capsule. Sometimes, however, the capsule may be 
completely changed before the disappearance of the pseudopodia. 
Probably, in rapid explosion, the two take place simultaneously. 
Changes in the capsule 
For the interpretation of the entrance of the spermatozoon 
into the egg the transformation of the capsule is much more 
important than the changes in the protoplasmic cup. We will 
therefore follow the capsular changes very carefully. The first 
change is the out-pushing of the outer cavity of the inner tubule 
(compare fig. 61 with 67). Here it is evident that the wall of 
the outer cavity of the inner tubule has been everted, while the 
wall of the inner cavity (fig. 61, 7.¢.c.) has been stretched. It is 
difficult to see just what change has taken place at this time 
in the central body. In some instances it appeared that it had 
been lengthened, and in some specimens I thought the end of 
