192 



WILSON. [Vol. I. 



made by fixing with Perenyi's fluid, staining with the ordinary dilute iodine solution 

 used in the study of vegetal tissues, and ''learing, first, in dilute, afterwards in strong 

 glycerine. The color fades in a few hours, when the specimens may be stained with 

 the carmine-solutions and sectioned or mounted whole in glycerine or balsam. 

 Perenyi's fluid is the only fixing fluid, so far as my experience goes, that causes abso- 

 lutely no shrinkage. In studying any but the very early stages, it is necessary to 

 remove the hardened mass of albumen from the alimentary canal. This operation 

 (which requires some practice) may best be performed under glycerine with a pair of 

 fine pointed scalpels, the dorsal wall of the body being cut away.] 



EXPLANATION OF PLATE. 

 I have made many actual sections that clearly demonstrate the relations shown in 

 Figs. 3, 4, and 5, but it is preferable to figure optical sections, since they show the 

 structure with equal clearness, and better preserve the natural relations of the parts. 

 For making actual sections it is usually necessary to remove the contents of the 

 mesenteron, a process which often mutilates the entoblast. 



np. Nephridia. 



o.g. Oral gland. 



pg. Supra-oesophageal ganglion. 



r'. Neural row. 



r2. Nephridial row. 



r^. "Outer row." 



si. Inner series of setigerous glands. 



so. Outer series of setigerous glands. 



vn. Ventral nerve-cord. 



X. " Lateral teloblast." 



X. Anterior continuation of the "outer 



c. Large ciliated cells of the ectoblast, 



extending along the ventral median 

 line. 



d. Dissepiments. 

 £c. Ectoblast. 

 en. Entoblast. 



/m. Longitudinal muscle-fibres. 

 m. mouth. 



3f. Primary " mesoblast." 

 mes. Mesoblastic cells. 

 JV. Neuroblast. 

 n. Neural row. 

 A^p. Nephroblast. 



Fig. I. Diagrammatic view of the hinder part of the germ-bands of an oval 

 embryo, seen from the ventral aspect, showing the eight teloblasts, the mesoblastic, 

 neural, nephridial, and " outer " cell-rows, and part of the ectoblast. 



Fig. 2. Camera drawing of part of the v€ntral view of an embryo in the same 

 stage as the last, showing the six anterior teloblasts, the neural, nephridial, and outer 

 cell-rows and part of the ectoblast. At mes. is shown a row of mesoblastic cells that 

 give rise to longitudinal muscle-fibres. 



Fig. 3. Optical longitudinal section through an embryo somewhat older than that 

 from which Fig. 2 is taken. Camera. 



Fig. 4. Optical transverse section through a slightly older embryo, showing the 

 nephroblasts and outer teloblasts, with the overlying mesoblastic bands. Camera. 



Fig. 5. Optical transverse section in front of the last, showing the neuroblasts, 

 nephridial rows, and outer rows. The precise relations of these structures to the 

 ectoblast and mesoblast are shown. Camera. 



Fig. 6. Diagrammatic view, from the ventral aspect, 'of the germ-bands of an 

 embryo about the middle of lai-val Hfe, after disappearance of the six anterior telo- 

 blasts. To show the relation of the eight cell-rows to the adult structures which 

 appear in the anterior part of the figure. The figure is made diagrammatic for the 

 sake of clearness, but is a fair representation of the actual appearance of the 

 preparation. 



Fig. 7. Constructed from two consecutive longitudinal sections through the pos- 

 terior part of an embryo somewhat younger than the last. It shows the entoblast 

 and ectoblast, one of the mesoblasts, and the beginning of the mesoblastic and neural 

 rows. The neuroblast has disappeared. Camera. 



