Cytology of the A sczts. 547 
substance from the centrosome. It was suggested in an earlier paper ( 9 ) 
that such changes might be due to the action of an enzyme. 
There appears to exist a somewhat complete gradation of forms from 
those in which the activity of the centrosome is the only force at work 
to those where vacuoles delimit — or help to delimit — the spore. In the 
latter cases we are inclined to regard the changes around the centrosome as 
ultimately responsible also for the vacuoles. 
Summary. 
1. The divisions in the ascus have been investigated in Htimaria 
granulata , Ascoholus furfur aceus, and Lachnea stercorea ; in each of these 
species previous investigations showed that a pseudapogamous fusion 
occurs in the ascogonium, and a subsequent asexual fusion in the ascus. 
2. In each the first division in the ascus is heterotype, the second 
homotype, and the third brachymeiotic. Two reductions in the chromo- 
some number thus occur in the ascus of each species, and afford independent 
confirmation of the two successive fusions previously described. 
3. The number of chromosomes in the first division in the ascus 
is eight in Humaria and Ascobolus , and four in Lachnea . After brachy- 
meiosis is complete there are four chromosomes in Humaria and Ascobolus , 
and in Lachnea two. 
4. Pairing of the chromosomes which are to separate in brachymeiosis 
takes place in the second prophase in Humaria and Ascobolus , but does not 
occur in Lachnea. 
5. In Humaria the chromosomes brought together in fertilization are 
found to be paired in the division preceding meiosis. 
6. The meiotic prophases were studied in some detail in Lachnea ; the 
parts of the bivalent chromosome are united end to end, and separate 
transversely. 
7. In the first ascus division in Lachnea two long chromosomes and 
two short ones may be constantly recognized, and in the third telophase, 
after brachymeiosis is complete, one long and one short chromosome. 
8. The delimitation of the spore in Lachnea depends on altered 
substance flowing out from the centrosome. This is less evident in Asco- 
bolus where vacuoles play an important part in spore-formation. 
Pp 
