A STUDY IN MORPHOLOGY. 6.3 



them, much less than 1 per cent., are found to have eggs attached to their limbs when 

 the collection is examined. 



If the mature animals could be induced to thrive and multiply in confinement, there 

 would be no difficulty in obtaining a sufficient supply of eggs, but until this can be 

 done it must be extremely difficult to procure them in sufficient numbers for exhaustive 

 study. 



During the early stages the eggs are so delicate that they are soon destroyed by 

 the confinement and compression to which it is necessary to subject them while they 

 are under examination, and it is therefore impossible to watch very many stages 

 in a single egg. 



When we add to this that the eggs are laid about 9 o'clock in the evening, and 

 must be studied between this time and daylight, after several hours of laborious 

 collecting, by eyes that have been already severely taxed with looking over the collec- 

 tions and picking out the transparent and almost invisible adults by an artificial 

 light, and examining each one of them with a lens to find those which carry eggs, the 

 difficulty of the subject will be appreciated. 



The eggs are spherical, transparent, and they contain extremely little food- material. 

 This is uniformly distributed over the whole egg in minute globules, which have nearly 

 the same colour and refractive index as the sunminding protoplasm. 



The egg undergoes total regular segmentation, and a true segmentation cavity 

 occupies the place filled by the large central yolk-mass in the eggs of other Arthropods. 



It first divides into two equal portions (Plate 1 , fig. 1 ) ; then, by a cleavage at 

 right angles to the first, into four (fig. 5) ; then into eight (fig. 8) ; then into sixteen 

 (fig. 10) ; and so on. 



At the stage shown in fig. 10 the inner ends of the sixteen spherules are seen to be 

 separated from each other by a central space, the segmentation cavity, which persists, 

 and is shown at later stages in figs. 11, 13, 15, 16, 17, 19, and 20, at b. 



In fig. 10 the egg will be seen to be spherical, and all the segments have their 

 broad ends at the surface ; but in the next stage one pole of the egg becomes a little 

 flattened, and in an optical section the spherule (c), which occupies the centre of the 

 flattened area, is seen to have its broad end nearest the centre of the egg. 



Most of the food-material has meanwhile disappeared from the other spherules, 

 which are now quite transparent, while the spherule (c) still contains as much as 

 ever, but apparently no more than there was contained at an earlier stage in an equal 

 area of any part of the egg. In an optical section of the same egg, in a plane at right 

 angles to that of fig. 11, the spherule (c) shows a trace of a fissure, which a little later 

 divides it into two (see fig. 12, c). 



Plate 2, fig. 13, is an optical section, like the one given in fig. 11, of a somewhat 

 older egg; and fig. 14 an optical section of the same egg at right angles to fig. 13. 

 The outline is a little more flattened on one side than it is in fig. 11, and the 



MDCCCLXXXII. K 



