45 



We have now to deal with several 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 laying 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 larvse 

 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 (pi. X, fig. 4 a; pi. XI, fig. 3 c). 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. 3 a and fig. 3 c in pi. Ill with that 

 between fig. 4 a and fig. 4d in the same pi. 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 larvse that come out of the eggs in more than half of my species, as the 

 length of these larvse 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 

 larvse: those of Sphcer. 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 Stenolhocheres egregius (pi. I), Homoeoscelis 

 minuta (pi. II), and especially in Horn, mediterranea (pi. 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 Sphcer. Calliopii (pi. Ill) and in the two species of Choniostoma 

 (pi. X and pi. 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 



