486 JOSEPH STAFFORD, 



Dot look like glandular cells. Nevertheless it is quite possible that 

 some of these cells metamorphose into glands. 



From the study especially of surface sections, where a number 

 of these nests of cells can be seen in relation to one another, it was 

 suggested to me that they might be centres of cell reproduction, or, 

 at any rate, represented a district of retarded differentiation. The 

 latter case would presuppose the formation of the total number of 

 cells before the division of labor came into play ; or, in other words 

 there would be in the growth of the animal a period of cell-reproduction 

 and then a period of cell- differentiation. That this is not true scarcely 

 requires proof, but a comparison of sections through developing 

 animals of different ages leaves it beyond question. In a section of 

 the embryo through the pharynx 1 could count: in the pharynx 12 

 to 15 nuclei, outside of the pharynx 40 to 50 nuclei ; while to count 

 the nuclei that appear under the same conditions in a section of the 

 adult is no easy task. The pharynx alone in such a case shows by 

 focussing up and down about 80 nuclei belonging to the still re- 

 maining cells. 



But in the adult animal evidence is not lacking. Horizontal 

 sections through the posterior end e. g. show admirably how the 

 peripheral parenchym-cells gradually pass over into the 

 ordinary body-parenchyma (endoparenchyma). In some pre- 

 parations are exhibited even early stages of vacuolation and increase 

 of size forming transitional stages to the underlying tissue. In this 

 region, where there are no organs in immediate proximity, and which 

 is likewise tolerably free from parenchyma-muscles, the ground tissue 

 has so far retained its original cellular character that almost every 

 cell contains a centrally situated nucleus and a tlakey protoplasm. 

 The cell-boundaries, too, increase in size and loose their regular, 

 compact form as we pass inwards. Deeper and further forwards, 

 however, bordering on the intestine and genital organs the structure 

 is different. In this region is found the great mass of locomotory 

 muscles, and here, too, the different parts of the body are much 

 more extensively and energetically changed in positions. Corresponding 

 with this, one finds a greater plasticity of the ground tissue, and a 

 greater variation in the contour of its cells depending upon the 

 direction and state of contraction of the neighboring muscles. The 

 cells also loose their cellular character to a great degree. The nucleus 

 is generally absent, the protoplasm forms a reticulum with larger spaces 



