396 DAVID H. TENNENT 
The study of the sections of the preserved material was more 
easily made than was the study of the artificially parthenogenetic 
material. The evidence from this material seems to show con- 
clusively that there are two classes of spermatozoa with respect 
to the V-shaped chromosomes, one class with one V, the other 
with two. 
In fig. 5 one V and the long rod are shown. The number of 
chromosomes in each plate is 18. In fig. 7 two V’s and the long 
rod are evident, 19 chromosomes are present. In fig. 8, one V 
with the arms separated, one V with the arms in contact and the 
long rod. Probably 19 chromosomes are present. 
II 
While working with the phase of the question just described 
it occurred to me that possibly conclusive evidence might be given 
by segmenting eggs from crosses between Arbacia punctulata, in 
which as I showed in 1907, the chromosomes are all small, and 
Toxopneustes, in which the chromosomes are larger. 
I succeeded in making this cross for the first time during the 
past summer (711). Up to that time I had not been able to secure 
a usable percentage of fertilizations by either the Hertwig method 
or the Loeb method, but by combining the two methods I 
obtained fertilization in a fair number. 
The Arbacia eggs were allowed to stand in sea water for four 
hours, then transferred to 400 cc. sea water + 8 ec. +, NaOH for 
five minutes, and then Toxopneustes sperm added.  Fertiliza- 
tion membranes were formed on from 50 per cent to 90 per cent 
of the eggs, in different lots. 
Toxopneustes eggs were allowed to stand in sea water for two 
hours, then placed in 400 ce. sea water + 6 cc. 4 NaOH for five 
minutes and Arbacia sperm then added. Fertilization membranes 
were formed on about 10 per cent of the eggs. 
Numerous experiments showed the durations given to be the 
best. From these fertilizations only a few embryos developed to 
the pluteus stage, and all of these showed their hybrid: origin. 
The skeleton was of ‘an intermediate type. Most of the embryos 
