ON THE ANATOMY OF HLSTKIOEDELLA HOMARI. 337 



sometimes far back at the caudal end of the ovary, they have 

 to move some considerable distance forward before they can 

 find exit through the oviducts. In passing through the 

 second ampulla the egg is surrounded by its capsule, which 

 binds it firmly to the membranes of the lobster's ova, or the 

 hairs of the carapace surface of the branchial chamber. 



I have already drawn attention to the fact that the oocyte 

 commences to prepare for the first maturation division and 

 the extrusion of the polar bodies when it has acquired only a 

 portion of its yolk material. It is noteworthy that only one 

 of the oocytes undergoes this change at a time. It is the 

 most advanced and the largest. While the amphiaster is 

 seen in this egg, I have never observed it in any of the 

 younger ones, although some of these to all external appear- 

 ances are as large and as mature as the one in which it has 

 appeared. 



As the oocyte prepares for maturation its staining reaction 

 changes. Up till this time the superficial layer ot" its cyto- 

 plasm stains darkly, while the deeper portions surrounding 

 the nucleus do not take the stain. With the appearance of 

 the maturation spindle the staining reaction of the cytoplasm 

 becomes uniform throughout the cell. 



The first sign of approaching maturation is announced by 

 the changes undergone by the nucleus. It is distinguishable 

 in the living egg as a clear spot in the middle of the dark 

 graimlar cytoplasm. By a number of changes, which I have 

 not followed in detail, the chromosomes form, the germinal 

 vesicle breaks down, and the amphiaster of the first polar 

 body forms. This at the moment it appears is very small, but 

 grows rapidly with the growth of the egg. From the time it 

 appears to the time it reaches its full dimensions it at least 

 trebles its length, while the egg grows considerably in size. 

 From measurements made of the length of the central spindle, 

 from centi-osome to centrosome, and the diameter of the egg 

 in its longest axis, it was found that from the time the central 

 spindle was clearly visible to the time it ceased to grow it 

 trebled its length, while the egg a little more than doubled 



