DEVELOPMENT OF PLATYPHYLAX. 57 



1.5 mm. in length. Glands from such larvae show very clearly 

 the two rows of cells forming the wall of the gland, and the ad- 

 dition of a little dilute methyl green to a drop of normal salt 

 solution containing them shows at once that the nuclei are of a 

 simple, unbranched type : typically the nuclei are round at this 

 stage, though a few are slightly elongated. It may be noted here 

 that from the time of breaking out of the egg membrane to the 

 time of emergence from the mass of jelly containing the eggs 

 may be some hours for an individual, and 24 hours barely suffices 

 for a brood to get clear of the jelly after the first ones are seen 

 moving within the mass. To distinguish carefully in every case 

 between those larvae fresh from the egg membrane and those 

 just out of the jelly would be rather more laborious than results 

 would warrant, so in speaking of larvae just hatched I mean larvae 

 in the jelly or out of it only a few hours. 



In each of the round or slightly elongated nuclei of this first 

 period there is, almost without exception, a single nucleole pres- 

 ent (Figs. I and 2). This nucleole is large, round or elongated, 

 smooth in outline, lies near the center of the nucleus, takes the 

 stains characteristic of the nucleoles of ordinary cells, and, in 

 short, is undoubtedly a true nucleolus. A study of fresh glands 

 of larvje just out of the egg or even yet within it, shows that 

 the elongated (rarely divided) nucleoles belong generally to the 

 larvae which have been for some time out of the egg. 



Larvai which have been out of the jelly for twenty-four hours, 

 and which have been supplied with sand, possess a well con- 

 structed case. Glands from such larvae contain a larger propor- 

 tion of elongated nuclei, the elongation being transverse to the 

 long axis of the gland. In whole preparations there may be 

 found single round or elongated nucleoles, and, in many instances, 

 two or three nucleoles in one nucleus (Figs. 3, 5, 6). Sections at 

 this stage show that the two nucleoles in a nucleus arise df divi- 

 sion of the original one, since various stages of elongation and 

 constriction, giving more or less dumb-bell-shaped figures may 

 be found. By division here is riot meant bipartition necessarily, 

 but fragmentation, since evidences of the latter process are 

 readily observable (Fig. 4). From this time on the nucleoles 

 are more ragged and irregular in appearance, but this may 



