THE SPERMATOPHORE IN ARENICOLA 1035 
those parthenogonidia found in the Volvox colony. Max Hart- 
mann, in describing the reproduction of the Dicyemidae, speaks 
of this central cell as the agametangium because in it develop the 
asexual, or as he calls them, the ‘agamic’ individuals. After 
several generations of these agamic individuals, there arise the 
sexual or the gametic individuals. They arise from the embryo 
cells (Keimzellen of Hartmann) by a process of cleavage very sim- 
ilar to the development of the agamic individuals, except that in 
the female the reproductive cells are split off early. The female 
as well as the male sexual individual grows within the asex- 
ual parent. The eggs are developed from the embryo cells of the 
female. They are freed from the gametic individual into the so- 
called agametangium of the agamic individual by the death of the 
gametic form. The egg matures by forming polar bodies and is 
fertilized by sperm which have discharged from the male gametic 
individual by its death and disintegration. 
To harmonize Hartmann’s description with the language I have 
used in giving the alternation of generations in the Arenicolidae I 
have only to change his terms slightly; (I have adopted the ter- 
minology proposed by Beard, cited later). Call his agamic in- 
dividuals the sporozoon and the Keimzellen spores; his gametic 
individual, the gametozoon; then the dicyemids make concrete 
our conception of how the alternation of generations of the higher 
forms arose from such simple ones as Volvox, even though the 
line of ascent may not actually have passed through the Dicye- 
midae. 
Imagine that in a Volvox-like form the sexual colony or gameto- 
zoon develops eggs and sperm before it is discharged from the 
colony which reproduces asexually and the condition of the dicye- 
mids is practically achieved. Now imagine that a regular alter- 
nation of generations is established instead of the intercalation 
of an occasional sexual generation in the midst of the dominant 
asexual reproduction of the Dicyemidae and a condition is estab- 
lished that needs little if any modification to give the alternation 
of generations as we find it in the Arenicolidae, as follows: 
The adult Arenicola, a sporozoon, corresponds to the sporophyte 
colony of Volvox or the agamic individual of the dicyemid. At 
