45 
We have now to deal with sevéral other questions, some of which are difficult to 
answer definitely, namely: the size of the ovisacs compared with that of the females in the 
different species, their relative size in females of the same species and of different species, 
the number and size of the eggs in the ovisacs of the different species, and the fertility of 
each species. Here, however, we at once meet two difficulties: the one mentioned above 
on p. 24, that shortly before her laymg eggs the female is always somewhat (and no doubt 
usually much) larger than after it, and in most cases it is quite impossible to procure spe- 
cimens which are going to lay eggs, such as have half done and such as have quite done 
laying eggs; most frequently one only finds from two to five specimens altogether, all of 
which have half done or quite done, or else one or two of them are not full-grown; besides, 
an ovisac is somewhat smaller when it has just been laid, than later on, when the larve 
break out of it, for during the development the ovisac increases somewhat in size, 
getting at the same time less firm, as each egg, which is always globular or polyhedrous 
at the beginning, becomes elongated. Making allowance for this fact, it is seen that in 
most species there is not usually much difference between the sizes of the ovisacs deposed 
by the same female, whereas in some species the ovisacs often, though not always, differ 
very much in dimension (pl. X, fig. 4a; pl. XI, fig. 3c). There is a great difference, on 
the other hand, between the average size of the ovisacs compared with the adult females of 
each species; comp. e. g. the proportion between fig. 3a and fig. 3c¢ in pl. LIT with that 
between fig. 4a and fig. 4d in the same pl. Of course, we may say that as a rule the 
ovisacs are comparatively smaller in the species which depose a very large number of them 
than in those which lay rather few, yet even in these the ovisacs sometimes do not exceed 
middle size. In the species whose females are large, as a matter of course, the ovisacs are 
much larger than in the small species. 
The number of eggs contained in the ovisacs naturally depends on the size both of 
the eggs and of the sacs. It is true, I have not measured the eggs of various forms, but 
as I know the larve that come out of the eggs in more than half of my species, as the 
length of these larve varies between about ‘15 mm. and -30 mm. only, and as they show no 
relatively great differences either of breadth or thickness, I possess a pretty accurate standard 
for judging the relative size of the eggs, for, evidently, the largest eggs (judging from the 
larve: those of Spher. decorata and of the genus Choniostoma) cannot be much more than 
double the diameter of the smallest (in the genus Homoeoscelis). The further result is, that 
in the species whose females are very small, as Stenothocheres egregius (pl. 1), Homoeoscelis 
minuta (pl. Il), and especially in Hom. mediterranea (pl. XIII), the eggs must by very large 
compared with the females, whereas the eggs must be proportionally small where the females 
are very large, as in Spher. Calliopi (pl. IIL) and in the two species of Choniostoma 
(pl. X and pl. XI). That these statements agree with facts appears very clearly from the 
illustrations of the eggs and females of the above-mentioned species; — it must be borne 
