waite: antennal glands in iiomarus americanus. 175 



lu an embryo about 22 to 24 days old (September 5tli),^ represented 

 by Figure 17 (Plate 2), the spheroidal form of the endsac is well marked 

 (Plate 2, Fig. 23, sac. trm.). At this stage, however, when there are 

 twelve nuclei, it is not visible from the ventral surface of the appendage, 

 nor is there any circular or crescentic arrangement of nuclei and cells at 

 the base of the appendage, such as several authors figure as representing 

 the first trace of the antennal gland. Such an appearance accompanies 

 the ectodermic invagination, of which there is as yet no trace, either in 

 surface view or in sections. 



In an embryo from the same brood two days older (September 5th to 

 7th) there appears in sections a definite vacuole (Plate 2, Fig. 24, vac.) 

 situated centrally in the endsac, which here has only nine nuclei. This 

 vacuole has a smooth distinct outline, which is evidence that it is not an 

 artifact. It is clearly not intercellular, for there are no cell membranes 

 near it. From this stage on there are seen in the endsac of each indi- 

 vidual a few well marked vacuoles of various sizes (Plate 2, Fig. 22, Plate 

 3, Fig. 26). 



It seems probable that the lumen of the endsac originates by the con- 

 fluence of the vacuoles' of the syncytium. I can therefore agree with 

 Kingsley ('89, p. 29) that the lumen of the endsac is neither an enclos- 

 ure of part of the body cavity nor in any way connected with it. A pro- 

 cess parallel to this is described by Bergh {'S8, p. 228) in the formation 

 of the nephridia of Criodrilus. 



It is interesting to notice that the formation of the lumen of the end- 

 sac begins before there is any trace of the ectodermic invagination, and 

 only eight days (August 30th to September 7th) after the earliest differ- 

 entiation of the endsac is seen, whereas in Palsemonetes (Allen, '93, 

 p. 338) the lumen of the endsac does not appear until early in larval 

 life and is there intercellular. 



The next stage to be noticed is from another series. It is slightly 

 older than that figured by Herrick ('95) in Cut 34, Plate I., and between 

 Stages and P of Bumpus ('91, PI. XIV.). The tip of the telson has 

 grown cephalad until it is somewhat in advance of the base of the second 

 antenna ; there is no pigment in the eye. There have elapsed since fer- 

 tilization, to judge from a comparison with Herrick's figures, 23 to 25 

 days, but the actual interval is greater, — probably 28 to 30 days, — as 



1 This embryo was from the same brood as that from which Figure 16 was 

 drawn, showing the earliest recognized condition of the endsac. Since the younger 

 was killed on August oOth, and the older on September 5th, there is an interval of 

 six days between the two. 



