Free-swimming Nauplius of Leptodora hyalina (Lillj.). 217 



later date (fig. B), the cells of the end-sac have become smaller, and 

 there is a more distinct basement membrane; they greatly resemble 

 the cells of the end-sac of the maxillary gland. In an older nauplius 

 (fig. C) the intracellular duct begins to disintegrate, but the end-sac 

 remains adhering to the dorsal ectoderm for a very considerable time 

 ultimately, however, it disappears. 



Fig. 6. — A. The antennary gland seen in transverse section through the youngest 

 nauplius at the level of the 2nd antenna. 



B. The same gland seen in a slightly older nauplius. The cells of the 

 end-sac are smaller, and there is a more definite basement membrane. 



C. The same in an advanced metanauplius. The intracellular duct no 

 longer communicates with the end-sac. 



According to these observations, the maxillary and possibly the 

 antennary glands are purely ectodermal in origin, and the end-sac is 

 to be looked upon as merely a terminal thin-walled dilatation of the 

 glandular tube. At one time I believed that mesoderm crept up 

 behind the maxillary gland (see fig. 4, A), and formed the end-sac, but 

 renewed observation convinced me that it is formed out of the ecto- 

 derm in direct continuity with the glandular tube (see fig. 3, B). 



It appears from recent observations that the nephridia of Chseto- 

 pods should be regarded as ectodermal tubes which generally open 

 into a ccelom, and sometimes may come into connection with a 

 generative funnel. In a trochosphere (e.g., in that of Polygordius), 

 the "head-kidney" is probably budded off from the ectoderm, and 

 since there is no ccelom into which it can open, the tube terminates in 

 a slightly dilated " flame-cell." 



Although ccelom sacs are doubtless formed in the development of 

 some Crustacea, yet I altogether failed to discover any traces of them 

 in the youngest nauplius of Leptodora that I have examined; and 

 even in those cases where they have been described, it does not follow 

 that the antennary and maxillary glands enter into relationship with 

 these transitory ccelom spaces. 



