216 Prof. E. Warren. On the Development of the 



swelling on each side. In the lateral thickening of ectoderm, a band 

 of cells passes nearly vertically downwards to the papilla representing 

 the second maxilla. The band will become the exit-dnct of the future 

 gland : the band extends upwards into the dorso-lateral swellings 

 mentioned above (fig. 3, A). It is out of these swellings that the rest 

 of the gland becomes differentiated. 



Fig. 3. B is a cross-section a little posterior to A, and is taken 

 from a nauplius very slightly older. Here the end-sac can be seen 

 vaguely marked out from the surrounding ectoderm. 



The lateral swellings containing the developing glands gradually 

 extend upwards, and after a time they meet together in the mid-dorsal 

 line (fig. 2). 



There is formed simultaneously a deep transverse groove in front of 

 the upgrowing swellings, and a less conspicuous groove occurs behind 

 (fig. 4, A and B). 



The overhanging portion of the embyonic carapace (fig. 4, B) will 

 be carried backwards as the animal develops, and will, in the female, 

 expand into the free portion of the carapace overhanging the first two 

 abdominal segments. 



As the fused swellings (the embryonic carapace) gradually extend 

 backwards over the dorsal surface of the thorax, the maxillary gland 

 is drawn out with them into the position and shape seen in the adult. 



At the same time there is a general expansion of the parts ; the 

 maxillary gland begins to separate itself from the surrounding ectoderm 

 (figs. 2, 3, 4, and 5, f), and the space around the heart gradually 

 increases. There is also a certain amount of disintegration of the 

 ectoderm where the dorso-lateral swellings met in the middle-line. 

 The spaces marked * in figs. 2, 4 and 5 are thus formed, and ultimately 

 they become continuous with the space around the heart. 



We have already seen that this pericardial space has a definite floor 

 of flat mesoderm cells, but the roof would seem to be simply the 

 ectoderm of the body-wall. The exit-duct with the external opening 

 travels upwards into a dorso-lateral position, so that in the adult it is 

 nearly horizontal. 



In the material at my disposal it is not possible to decide for certain 

 whether the antennary gland also arises from the ectoderm, but it is 

 highly probable that it does so. 



Fig. 6. A, B, C represent three stages in the growth of this struc- 

 ture. The nuclei in the intracellular duct, and connected ectoderm 

 have been carefully put in the diagrams from actual sections, and their 

 arrangement certainly gives the impression that the duct should be 

 regarded as an ingrowth of ectoderm. 



Fig. A represents the condition observed in the youngest nauplius. 

 The end-sac consists of fairly large cells which are not very different in 

 character from the cells forming the intracellular duct. At a slightly 



