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expelled by the genital aperture situated behind the ventral sucker. 
Other eggs may follow the first, but, according to our present know¬ 
ledge, the number of those present at a time remains limited to 5 or 6. 
When the female is impregnated the formation of normal eggs begins. 
At about this period we ought to expect the uterus to show, in its 
hindmost part, a number of terminahspined eggs, while the anterior part 
may still contain one or some lateral-spined ova. Such was the 
case in the specimen observed by BiLHARZ ; the analogy it presents 
to some of the Trematodes described above is complete. Had 
Bilharz happened to see the specimen an hour or a day later the 
last lateral-spined egg would have been laid ; the specimen would 
have been ‘ mature.' Had he happened to see it a day or a week 
earlier, no terminal-spined eggs might have been formed yet ; the 
specimen was ' immature.' As he actually saw it it was half 
‘mature’ and half ‘ immature.’ For the moment, therefore, I see no 
reason why my theory should be annihilated by the one accidental 
observation of Dr. Leiper, —admitting even that the egg m question 
were really terminal-spined, and did not only appear as such because 
the lateral spine was turned towards, or away from, the observer. 
Dr. Leiper himself says in the discussion (p. 45) that his obser¬ 
vation makes him believe ‘ that the explanation was not correct which 
relied solely upon immaturity as the cause of the lateral spine. This 
is quite right, but I have not pretended either, that immaturity is the 
sole cause of the lateral spine. Dr. Sambon. in quoting my theory, 
makes me say that ' the eggs bearing a terminal (obviously a misprint 
for " lateral ”) spine probably represent the product of unfertilized 
females.’ He thus does not notice that there is a slight but very 
important difference between saying ‘ lateral-spined eggs are the 
product of unfertilized females,’ and saying, as I really have done, 
that ' unfertilized females are not capable of producing other than 
abnormal eggs.’ As a matter of fact, several earlier authors have 
pointed out how fertilized females might, under certain conditions, 
produce lateral-spined eggs also. These suppositions have up to the 
present day not been proved as true, but they have not been disproved 
either, and it is at least not impossible that what those authors 
surmise may actually happen. At any rate, I have never pretende , 
und do not pretend, that immaturity is the sole cause of the later 
spine; nor is it impossible that immature females, although producing 
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