106 MR. NEWPORT ON THE ORGANS OF REPRODUCTION, 



appearance of an air-bubble; it projects from the surface of the yelk, and the cavity 

 in which it is inserted. When viewed laterally, in those ova which have been first 

 placed in spirit, and afterwards in water, it is very much elevated above the yelk into 

 part of the clear space. In one instance I observed on the upper surface of this 

 vesicle an aggregation of globules, apparently oil-globules, about six in number. 

 Around the yelk, after the egg has been placed in water, there is a free space, as in 

 the immature ovum. When the perfect ovum, soon after its impregnation and depo- 

 sition, is placed for a few minutes in rectified spirits of wine, it begins to collapse on 

 one side in the long axis of the egg : that surface is thus rendered concave. Some- 

 times the egg contracts also at one extremity, but this is only to a small extent when 

 compared with the other. On watching this contraction of the egg and its yelk 

 beneath the microscope, while it remains in rectified spirits of wine, the yelk is seen 

 to retire from the shell towards the centre of the egg ; and its external surface ac- 

 quires a translucent appearance, resembling the albuminous space in the egg of the 

 Bird. During this contraction, it may be seen, through the sides of the yelk, that 

 the cells are of an uniform size, and retire slowly towards the centre. When the 

 egg has remained about half an hour in rectified spirit, the whole interior has become 

 translucent, although it is perfectly opake in the natural state, excepting a small 

 part near the centre, the locality of the germinal vesicle. That those parts of the 

 shell which collapse are the thinnest is proved by several observations. If the egg, 

 when entirely contracted, is put into cold water, it again becomes opake, and the 

 shell expands to its original dimensions and form ; but the yelk does not change its 

 appearance, it retains the shape it has taken in the spirit. From this expansion of 

 the shell we may reasonably conclude that fluid is imbibed through it, and occupies 

 the space between it and the yelk, and that this space is lined by distinct membranes ; 

 the memhrana vitelli before noticed in the early stages of the ovum, and the mem- 

 hrana externa or chorion {b) that lines the interior of the shell. These membranes exist 

 in the egg at the period when the embryo is complete ; the membrana externa, or 

 proper chorion, still lining the interior of the shell, and the membrana vitelli con- 

 stituting the amnion which incloses the young animal. We are thus able to iden- 

 tify in these low forms of Articulata the parts that are known to exist in the most 

 perfect animals, and in addition to them, the external envelope or shell. It is worthy 

 of remark, that the whole of these structures are formed in the ovisac, in which, as 

 before shown, only one egg is secreted at the same time, and is then passed, com- 

 plete in all its parts, into the oviduct, to be impregnated preparatory to the produc- 

 tion of the new being. 



3. Deposition of the Ova, and Habits of the Species. 



I have never yet seen the lulidae in coitu, but from the fact that the oviduct in the 

 female, at the season of depositing her eggs, is always completely filled with them, all 

 equally developed, as well as from the entire absence of a spermatheca, we may rea- 



