MUSEUM OF COMPARATIVE ZOOLOGY. 175 



same time (i. e. in rapid succession) is usually to be found in the com- 

 parative uniformity in size and shape which the individual eggs of the 

 group present. The greatest number observed which thus indirectly 

 gave evidence of belonging to a single deposit was thirty-seven ; on the 

 other hand, it is quite certain that a very small number may be deposited 

 at one time by slugs that are held in confinement. That the same is 

 true of unconfined animals, I can only infer from finding, now and then, 

 small groups or single eggs far removed from any others. 



The external surface of the egg is not smooth, but raised in almost 

 inperceptible bosses, which give to it the frosted look mentioned. Im- 

 mersed in water and examined under a low power of the microscope, 

 it is seen to be composed of a central, slightly yellowish, homogene- 

 ous portion, much more nearly spherical than the whole egg, and of 

 two thick coats of investment, which are colorless, and give it rigidity 

 and a great degree of elasticity. The central mass occupies from two 

 thirds to four fifths of the diameter of the whole egg. The two envel- 

 oping layers are not of uniform thickness, and may become at one or 

 both ends exceedingly thin. The outer layer is composed of colorless 

 laminae, which are for the most part nearly concentric, although at 

 intervals they may become thinner and disappear. The cue is formed 

 from this layer alone. There may often be distinguished a half-dozen 

 principal laminae, and also, with a higher magnifying power, secondary 

 laminae of varying thickness, and often in large numbers. The inner 

 layer is likewise colorless and transparent, but shows no trace of lamina- 

 tion. When the outer layer is cut, it is found to be resistent and 

 elastic ; but the inner layer offers less resistance and is rather viscid. 

 The inner layer is separated from the central, yellowish mass by a very 

 firm, structureless membrane, which exhibits a great tendency to wrinkle, 

 especially when moisture is withdrawn from the egg. This firm structure 

 is the membrana alhuminis. The contained yellowish substance is viscid, 

 like the white of the hen's egg, and like it is albuminous. In the 

 freshly laid egg it appears quite homogeneous. It is called the albu- 

 minous envelope, but from its great abundance here its nature as an 

 envelope is not striking. In this substance are suspended two struc- 

 tures which are conspicuous in all freshly laid eggs when examined with 

 a sufficiently high power. One of these is tortuous, and usually ex- 

 tends from near the surface of the albumen to the vicinity of the other 

 structure. It resembles an irregularly twisted, or here and there con- 

 stricted, thin- walled tube. As I hope to make it the object of further 

 study hereafter, I will only add that it has been compared to the chalaza 



