372 
REPRODUCTION AND PAIRING. 
Reproduction in tlie inollusca is invariably sexual and entirely 
dependent upon the complete activity of the generative organs, as 
although the ovum without fertilization undergoes segmentation up 
to a certain stage, yet the stimulus of the male element is essential to 
successful and regnlar develoj)ment. 
Some of onr species are extremelj' prolific, as many as two million 
eggs lieing estimated by one observer as the annual production of a 
large Auodonfa cygnea, and although all our species by no means 
approach this enormous rate of increase, yet a sufficient number 
generally survive to enable the different species to maintain their 
gruiind, their multiidication being effectively counteracted by number- 
less enemies and dangers, otherwise we should in a short time be 
literally overwhelmed by the vast numbers annually developed. 
Pairing does not take place in the Pelecypoda or in the more 
archaic (Jastropods, which are unjirovided with the necessary organs 
for the purpose, but all jjhalliate species exercise this power, although 
in remarkably diverse ways. 
Fig. ()S8. — l.ove-m or co’inin?' of a slnistrai and dextral IIclix aspcrsfi Midi, modified 
from a nature sketcli by \V. H. Hcalhcote, K.L.S. 
The preludes to tlie sexual act vary in the different species, certain 
of the sings marching round and round in a slowly contracting circle 
and also mntmilly patting, caressing and fondling each other with their 
tentacles, labial lobes and egersidia, and devouring the mncus from 
each others boilies ; the Arions also coiij^ume the accumulated mucus 
upon the caudal gland of the prospective partner, which has probably 
some excitatory effect upon the animals and possibly hastens the 
desired conjugation. 
Some Helices during their preliminary manoeuvres not only make 
nse of their love darts, but mutually touch and caress with their 
