THE AMERICAN LOBSTER. 



215 



Cut 39 represents a median longitudinal section through the embryo shown in 

 fig - . 230, plate 51. Here the entire embryo is immersed in the yolk or in a thin coagulablo 

 fluid derived from it, through 'which it can be seen, while the cell plate touches the 

 surface in a narrow, bow-shaped area, but dips below again at its peripheral margin. 

 The cell plate beyond the confines of the thoracic-abdominal process and appendages 

 of the embryo consists of a single layer of very large cubical or columnar elements 

 gorged with yolk. In front and behind, the edges of this sheet unite to form a cul-de- 

 sac, so that the whole structure resembles iu form a flattened bag, which is partially 

 buried in the yolk, with which it communicates by the opening or mouth of the sac 

 below. The edges of the plate are curled over in the yolk, like one of the limbs of 



Cut 39. — Median longitudinal section through ab- 

 normal embryo shown in fig. 230, plate 51. Fixed 

 with picro-sulphuric acid, stained in Kleinenberg's 

 hsematoxylon, August 9, 1892. 



Cot 40. — Sagittal section through abnormal em- 

 bryo in early stage of development. Fixed in 

 piero-sulphuric acid, stained in Kleinenberg's 

 hseinatoxylon, August 9, 1892. 



AbT, thoracic-abdominal process. Deg., egenerating cells. ep.f., ingrowing fold of surface-epithelium. Mo, mouth 

 of stomodreum. Pit, pit formed by ingrowing fold, r, outward fold of surfacs epithelium, y.c, scattered cells in yolk. 

 y., food-yolk, abnormall3' covering embryo in cut 39. 



the letter S. Iu other respects the histology of this egg-nauplius embryo resembles 

 that of a normal form, except iu perhaps a great preponderance of degenerating cells. 

 In the embryo, the surface view of which is shown in fig. 228, plate 51, essentially the 

 same conditions are seen. These abnormal embryos which have just been described 

 are due in all probability to a disturbance of the normal mechanical conditions under 

 which the egg usually develops. It is quite probable that they could be artificially 

 produced, but no experiments have yet been made in this direction. 



I have noticed another interesting abnormal variation in the invagination stage. 

 (See 91). At a period nearly corresponding to that shown in fig. 255, plate 54, there 

 is a large irregular cavity or several communicating cavities in the depths of the egg. 

 This chamber contains very little yolk, and its wall is composed of cells which grasp the 



