602 ARTHUR THOMSON. 
than a mere reduction in nuclear mass (Strasburger) has to be 
attained. He asserts the probability of their general occur- 
rence, and on A priori grounds even in parthenogenetic ova, 
while he has, as we have noted, lately observed a polar cell in 
the summer eggs of certain Daphnoids. He further applies 
his theory of the two kinds of nuclear plasma, and the necessary 
extrusion of some of the non-germinal or histogenetic, to sper- 
matogenesis and to differentiating processes in plants. 
II. Fouuicutar CELts. 
Till within the last few years it has been the all but undis- 
puted opinion that the follicular cells, which so frequently 
envelop the ovum, originated entirely from outside, from 
adjacent germinal or non-germinal cells. Lately, however, it 
has been vigorously maintained that, in some cases at least, 
the follicular cells arise within the ovum itself, and, according 
to most of the supporters of this view, from the germinal 
vesicle. 
In a too-much overlooked research (1877) on the follicular 
and other cells of Tunicate ova, about which so much difference 
of opinion has prevailed, Fol clearly distinguished the granular, 
hardly cellular globules, doubly misnamed “ test cells,” from 
the nucleated definite follicular cells, described the latter in 
contact with the germinal vesicle and half way out towards the 
periphery, and maintained that they really originated from the 
nucleus and migrated outwards. Lubbock had, indeed, long 
before (1861), described a budding of the nucleus, and various 
observations, such as that of the presence of follicular cell-like 
bodies in the gitellus, may be capable of interpretation in 
harmony with Fol’s theory, but for definite statement and 
observation as to the origin of these cells he undoubtedly 
deserves the credit of priority. 
In 1880 Nussbaum asserted, for the first time, the origin of 
Vertebrate (Amphibia and Teleostei) follicular cells from a 
morula-like division of the germinal vesicle, followed by a 
centrifugal migration of the daughter nuclei. According to 
Sabatier, Cadiat described in 1881 the origin of the follicular 
