ECONOMIC RELATIONS, ANATOMY, AND UFE HISTORY OF GENUS I^ERN^A. l8l 



This formation of the egg differs from that of the Lernaeopodidae in that the egg 

 filaments are much larger, and while in the l^ernaeopods the terminal oocyte alone 

 develops with the rest of the filament still attached to it, here the whole filament breaks 

 up and its integral oocytes develop simultaneously. But the resultant egg is practically 

 the same in the two families. A thin and structureless vitelline membrane is distinctly 

 visible around the newly formed egg. Inside of it the entire substance of the egg is 

 made up of yolk globules evenly distributed throughout a matrix of finely granular 

 protoplasm. 



These globules are spherical or ellipsoidal in shape and differ but little in size; they 

 are loosely packed together without being flattened, and without leaving the vacuoles 

 seen in Lemaeopod eggs, although these appear later. (See fig. 20, pi. viri.) The egg 

 nucleus is a little ellipsoidal, comparatively large, and contains a single large spherical 

 nucleolus, without any chromatin granules. This nucleus is surrounded by a well-defined 

 membrane and may be situated indiscriminately anywhere within the egg, as were the 

 nuclei of the oocytes in the egg filaments. 



The eggs pass down the oviducts in a single or sometimes a double row, with prac- 

 tically no flattening at all, or when there is any, it is fully as often lateral as longitudinal. 

 This is very different from what is found in the other Lemaeids, where the eggs are packed 

 so tightly in a single row inside the oviduct that they are flattened lengthwise into thin 

 disks or wafers. And they pass out through the vulvae and assume the same shape 

 and arrangement in the external sacks. Here, on the contrary, they pass loosely into 

 the external sacks, where they are arranged in many rows, without any definite order 

 and without being at all flattened. 



There is no separate cement gland, but the posterior portion of the oviduct acts in 

 that capacity. From the vulva to about the center of the fifth segment the oviduct 

 is slightly narrowed and its walls are greatly thickened. Elsewhere structureless except 

 for the muscle fibers they contain, the walls here become definitely glandular and secrete 

 the cement substance. (See fig. 17, pl.vm.) At the point where this change in structure 

 occurs there is a constriction in the oviduct and also an S-shaped curve in its direction. 

 The eggs striking this constriction are fertilized and then pass through the glandular 

 portion in single file, being covered with a layer of the cement substance during their 

 passage. There is no semen receptacle connected with the oviduct, at least none is 

 revealed either in gross examination or in sections, and hence it is impossible to prove 

 just where the eggs are fertilized. Nor should we expect to find any, for the spermat- 

 ophores are fastened by the male directly to the vulvae, and their contents are dis- 

 charged into the oviducts. It is therefore only a question of how far up the oviducts 

 they go, and it would seem most reasonable to suppose that they reach the portion just 

 above the glandular walls. 



The sperm would not likely be mingled with the cement substance in the glandular 

 portion of the oviduct, and if the eggs were fertilized very much above this portion they 

 would not be fully matured. 



The cement substance forms a thick outer membrane around the egg, separated a 

 little from the vitelline membrane and stiffening into a tough covering. The egg sack 

 itself is formed of the same material, and inside of it there are no secondary walls sepa- 

 rating the individual eggs, as in the other Lemaeidffi. The two membranes covering the 

 egg are separated a Uttle, and this together with the loose arrangement of the eggs in 

 the sack secures enough free space around each egg to supply the requisite oxygen for 

 the developing embryo. 



