260 



THE AMERICAN NATURALIST [\^ol. XLI 



In larvae that have been in the first stage a few days and are 

 about ready to molt it is obvious that the radiating lines in the 

 posterior part of the telson are the glands secreting the setse which 

 will replace the marginal spines at the next molt. In a prepared 

 section of the posterior part of the telson of such a larva, figure 5, 

 the old cuticle is separated from the epidermis by a space across 

 which the tips of the forming setae pass toward the hollow bases 

 of the old spines. Each old spine has a new seta beneath it but 

 as there are also other setae the second larvae will have more setae 

 than the first had spines; the long plumes, however, figure 7, are 

 slightly fewer in the second larvae than the spines in the first. 



Each developing plumose seta seems a flat plate ending in a 

 fine central thread and with its edges frayed out in short fine 

 threads. The base of each is deep within the epidermal ingrowth 

 that forms the secreting gland. Each gland seems a row or rod of 

 cells, indicated by large nuclei in a common protoplasm in which 

 no cell walls were seen. The longitudinally striated base of the 

 plumose seta forms the axis of the rod of cells. The space between 

 the radiating glands was in part occupied by blood, staining, 

 like the setae, yellow, while the nuclei were red in borax carmine 

 and orange G. 



Similar, but less developed rods of cells were also seen in sections 

 of the internal buds of the sixth pleopods where they were forming^ 

 plumose setae that projected into a bag surrounding the pleopod. 



By April 24th, when some of the larvae had begun to molt, it 

 was evident that something was abnormal, as some larvae in both 

 the first and the second stages fell away from the mother and 

 died. The mother also died, April 28th. The hatching was pro- 

 longed more than is probably normal so that many first and sec- 

 ond stage larvae were found side by side for a few days. Some 

 of the young in the second stage remained with thv morluT for a 

 few days but made excursions away from her and apiiii returned 



is not certain that this w:is ncniuil in C. vlarkii. While upon the 

 mother these youno- held firmly with their ehehe, hut they let go 

 when the dead female was lifted out of the water. When upon 

 the bottom of a dish they were able to stand up and walk feebly, 

 and after a day, they swam backwards on their sides by flapping 



