17-4 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



is possible that there are two cells differentiated at the same time. 

 Sections preceding and following the one seen in Figure 19 show that 

 only two of these differentiated cells are present in this appendage 

 at this stage. In three other specimens also I have found only two 

 such cells, so that there is certainly a two-cell stage in the development 

 of this organ. These nuclei divide, but divisions are not necessarily 

 simultaneous, for I have found cases in which there are three, four 

 (Fig. 21), five, six, seven, eight, nine, and twelve nuclei present. In a 

 few cases mitotic phenomena are found in some of the nuclei, but in 

 most cases, even where an odd number of nuclei is present, there are no 

 mitotic figures. These nuclei are distinctly different from those of the 

 ectoderm and of the surrounding mesoderm in the appendage. There 

 can be no doubt about these differentiated cells being of mesodermic 

 origin. In another particular this region differs from the surrounding 

 mesoderm; although the nuclei increase in number, there is not a cor- 

 responding increase of distinctly separated cells. There are partial cell 

 walls (Plate 2, Figs. 19, 21, par. cl.), but the cell areas are not fully or 

 sharply defined by cell membranes. This condition is found in indi- 

 viduals which have been treated by one or other of several different 

 methods of killing, hardening, and staining ; it does not appear there- 

 fore to be due to the influence of particular reagents. 1 The result is a 

 partial syncytium, or cell complex, in which the nuclei are irregularly 

 distributed, but often show a tendency to take a peripheral position 

 (Plate 2, Figs. 23, 24). 



Bergh ('88, p. 228) has found a parallel condition in the nephridia of 

 Criodrilus. My results do not, however, agree with the condition found 

 by Boutchinsky ('95, p. 169, Tab. VI. Fig. 143) in Gebia, in which, as 

 he says, the cells at a similar stage are separated by distinct walls. 



In Homarus this syncytial mass has an even oval outline, the longer 

 axis of the oval lying nearly in the transverse plane of the body, but 

 directed obliquely laterad and ventrad at an angle of 20° or 30° with 

 the frontal plane. The evenly rounded outline of the mass is preserved 

 even where it is separated from the mesenchyme by only a thin layer of 

 mesodermic cells. This oval syncytium with its contained nuclei becomes 

 the endsac of the antenna! gland, and in the further description will be 

 so designated. 



1 It should, however, be stated that my material had been in alcohol for some 

 time, which may have caused disintegration of cell walls in this particular region. 

 The cell walls of neighboring regions, and of corresponding positions in other ap- 

 pendages, are however firm and distinct. 



