2G4 AYERS ON THE DEVELOPMENT 



Teleas is equivalent to the third stage which I have found parasitic in the eggs of Oecan- 

 thus niveus, and is the same as the larva of Metschnikoff ; furthermore that Ganin's second 

 larval form is only my " third stage " in process of ecdysis. For an excellent summary of 

 Ganin's entire paper one may consult Balfour (1). Packard has given a more detailed 

 extract in (35) and (3G). 



The earliest stage 1 of the parasite found in the eggs of Oecanthus was that of the com- 

 pleted blastosphere (pi. 23, figs. 23, 31). This perfectly spherical body consists of a shell 

 of small, short, cylindrical cells which encloses a colorless, finely granular fluid, possibly a 

 nutritive or yolk matter. At this stage there are no cell elements except those which 

 form this shell (Blastoderm of Metschnikoff — Embryonalanlage of Ganin). Soon amoe- 

 boid cells are budded off from the inner ends of these cells and make their way into the 

 contained fluid. They are usually much smaller than the cells of the blastosphere and are 

 irregular in form. Some of them appear destitute of any nuclear structure, but most of 

 them possess a small, sharply defined, eccentric nucleus. On one side of the blastosphere 

 the cells in a linear tract elongate causing a spindle-shaped ridge to be formed on the sur- 

 face. This increases in size until it is quite prominent, when there appears a median 

 furrow dividing it into symmetrical halves or folds. At each end the folds are continuous 

 with each other by means of a narrow, curved cross-fold. The growth of the folds is accom- 

 panied over the whole of the inner surface of the blastosphere by a cell proliferation which 

 is most active along the region of the folds or germinal band. There now appear at the 

 starting point of the folds two pairs of prominent thickenings (pi. 23, fig. 27), the head 

 folds. The anterior of these is the larger and ends abruptly in the germinal band. From 

 this point backward the band gradually thickens into an evident prominence (pi. 23, fig. 

 27) which probably marks the boundary between the thorax and abdomen. It 

 is now bordered en each side by shallow furrows, produced by thickened bands 

 running outside of and parallel to it. The germinal band extends over half the cir- 

 cumference of the blastosphere which now begins to elongate into the spindle-shaped 

 larva. In the meantime the amoeboid cells collect into a mass in the centre of the embryo 

 and form the endoderm. In pi. 24, fig. 1, is shown the relation of the parasite to the host 

 in this stage, while in pi. 23, fig. 35, is shown a cross section of a blastosphere magnified 

 800 diameters giving the mutual relation of the elements composing it In the young 

 blastosphere the elements are very small, thin-walled cells with the longest diameter radial 

 to the sphei-e (pi. 23, fig. 23); as seen from the surface they are polygonal in outline j 

 upon treatment with osmic or acetic acid they become spherical. In the youngest stage 

 following segmentation, they are arranged in a uniform layer with no appreciable difference 

 in the size of the cells ; soon, however, the cells in certain tracts begin to increase in size 

 and to proliferate, giving off from their inner ends amoeboid cells which go to form a layer 

 of cells of irregular sizes and shapes just beneath the ectoderm. As soon as proliferation 

 begins, the cells lose their uniformity of arrangement and cohesion, the least pressure being 

 sufficient to displace them. In sections of this stage are found cells of the size and char, 

 acteristic appearance of ectodermic cells lying just outside the ectodermal layer, although 



1 The egg lias not been seen but is probably of the usual product proves. Allowing the contents of the sphere to be 

 pedunculate form, with the colorless yolk not gathered into genuine yolk-matter, there is no evidence that the segmenta- 

 olk masses. The segmentation of the egg is total, as the tiou may not have been "superficial." 



