1880. } A Sketch of Comparative Embryology. 103 
exactly known. The part of the spindle in the egg-cell, returns 
to the center of the egg and becomes a nucleus-like body, now 
termed the female pronucleus. 
The egg-cell, therefore, divides into two parts, first, d egg 
proper with the female pronucleus, sec- et 
ond, the polar globules. The egg-cell 
has become not as a whole, but partly, 
areal egg, the ultimate female sexual 
product. Since the use of the term 
egg cannot be restricted, ànd since 
precision of nomenclature is, in this 
case, particularly desirable, I have pro- 
posed the name ¢helyd/ast for the female 
element. 
We pass now to the history of the _ Fis. 5.— Egg ot Rayi 
three- iy | site o: an hou after 
male elements, or spermatozoa, con- laying. Formation of the first 
cerning which the observations of nat- polar globule, after Hertwig, 
uralists have been even less satisfactory. The adult spermatozoa 
have, with a few exceptions, an elongated, almost thread-like 
form, Fig. 6, and consist of a shorter and thicker 
portion, the head, a, a short middle piece, ġ, and a 
filiform tail, æ, from which is suspended, in many 
vertebrates, a thin and very transparent undulating 
membrane, c. Innumerable modifications of this 
type occur by variations in the size and shape of 
the head and the length and thickness of the tail. 
In a few exceptional cases, as among the nema- 
tode worms, the spermatozoa exhibit absolutely no 
trace of this form, but are apparently constructed 
upon an entirely distinct type. A few species of 
invertebrates have two forms of spermatozoa. 
In a not inconsiderable number of invertebrates, ®© \ | 
we find so-called spermatophores. These are only Fıc.6.—Fresh 
bundles of spermatozoa enclosed in a protective ersan ar oe 
covering or shell (Fig. 7). In Cyclops this shell is maculosa, after 
Secreted by the efferent duct, around the sper- r ‘middle pone ae 
matozoa, just as the shell is secreted around the . 
eggs by the oviduct. The spermatophores of some ~ a 
oe exhibit a very FomPlnt es structure, and have curious 
orms 
