Insects' Eggs. 325 



to a small gate or opening, through which the worm is seen to 

 emerge forth. From a number of observations made on silk- 

 worms' eggs, I have not been able to satisfy myself of the 

 correctness of the particulars described by this observer, nor 

 have I seen the young worm make its way out at this precise 

 spot, but generally at a point much below it. Leuckart states 

 this depression, the micropyle, becomes at a certain period con- 

 verted into a funnel, which is directly connected with the 

 mouth of the embryo, and serves to convey nourishment from 

 without to ifc. I see no grounds for such a statement; because 

 in the silkworm's egg, instead of a depression at this point, we 

 have a nipple, and there can be no more necessity for leaving 

 this funnel-shaped opening for the nourishment of the embryo 

 catterpillar, than for that of the chick. There is no opening 

 for such a purpose in the ovum of the bird ; indeed the vitel- 

 line membrame appears to form a perfectly closed sac to the 

 yolk. In some eggs we appear to have an involuted portion of 

 membrane, indicating simply where either the formative pro- 

 cess of the outer membrane terminated, or the spermatozoa 

 passed in to fecundate the yolk mass.* 



The germinal vesicle is situated in the yolk mass, it is well 

 marked, and of a very large size, in the egg of the bee, while 

 the egg is yet in the ovasac. By preparing sections, after Dr. 

 Hallifax's method, I find that the germinal vesicle of this insect 

 is not situated immediately near, nor even below, the so-called 

 micropyle, but more to the side of the yolk, represented in Fig. 

 17, and just in the position which the head of the embryo is 

 found subsequently to occupy towards the end of the period of 

 incubation. The germinal vesicle is well marked ; its macula 

 is at first single, then becomes multiple. 



The egg membrane, or shell as it is incorrectly called, of 

 the moth and butterfly, is composed of three separate layers ; an 

 external slightly raised coat, tough and hard in its character ; a 

 middle one of united non-nucleated cells ; and an inner one clear, 

 dense, and homogeneous in structure, imparting a fine iridescent 

 glaze to the surface, such as we see and admire in the old glass 

 vessels exhumed from the ruins of Pompeii. 



In the silkworm's egg the outer membrane consists of an 

 inner reticulated membrane of non-nucleated cells, and an outer 

 layer, the cells of which are arranged in an irregular circular 

 manner, also non-nucleated, with a number of minute pro- 

 jecting interstitial hairs, or setse. This layer has probably 



* "As to the origin of the micropyle, it does not appear to proceed, as has been 

 supposed by Meissner, from the mere deficiency of the epithelium cells in a certain 

 space, and it is not dependent, either, on its pre-existence in the vitelline mem- 

 brane, but, according to Leuckart, it is found in the chorion before it appears in 

 the vitelline membrane." — De. Alien Thomson. 



