426 WESLEY K. COE, 



one must depend wholly upon stained sections. But the eggs of 

 certain other species , as , for example , Cerebratulus leidyi and 

 Micrura caeca from New England, are so much more transparent that 

 the general processes of maturation, fertilization, and early cleavage 

 can be followed in a single living egg without the use of stains. By 

 this means and by the use of acetic carmine, the interpretation of 

 the structures found in the stained sections can often be confirmed. 

 The extensive series of preparations which I have made of the eggs 

 of these New England species were not nearly as beautiful, however, 

 as those of C. marginatus. Consequently the following descriptions, 

 except those which have reference to the living eggs, are based chiefly 

 on preparations of the eggs of this last-named species, and from these 

 most of the figures have been drawn. 



Methods. 



A certain difficulty in the study of the development of many of 

 the large Heteronemerteans arises from the fact that they will not 

 deposit their eggs in captivity^). But this drawback is compensated 

 for by the readiness with which their eggs lend themselves to artificial 

 fertilization. To obtain material for artificial fertilization, it is only 

 necessary to cut open the animals and allow their genital products 

 to ooze out into the water, A large female is placed in a shallow 

 dish of perfectly clear water, and a longitudinal slit is made in its 

 dorsal surface on each side of the proboscis-sheath, and throughout 

 a considerable portion of the body. If the eggs are fully ripe, the 

 muscular contractions of the worm are sufficient to force them out 

 into the water in great numbers. The eggs are allowed to settle for 

 a minute or two when the water is replaced by fresh. 



As many spermatozoa as are desired may be obtained by punctur- 

 ing a ripe male in the back with a needle. It is much better to have 

 too few spermatozoa than too many, for in the latter case some of 

 the eggs are sure to be doubly fertilized and to develop abnormally. 

 Eggs fertilized under these conditions develop readily until they reach 



1) Large specimens (2 — 3 feet in length) of Cerebratulus lacteus 

 Veerill, which I have kept alive in the laboratory, retained their eggs 

 for more than two months past the time when they are normally 

 deposited. Finally the animals died without any perceptible change in 

 their ova. It was impossible to determine whether their eggs were 

 still capable of development as I had only females, and the males in 

 the waters of the Sound had long since discharged all their spermatozoa* 



