300 



Mollusca. 



snailsj the sexual apparatus possesses numerous .accessory organs, 

 albumen glands (which manufacture the albumen to surround 

 the eggs), mucous glands (which secrete mucus during copulation), 

 spermathecee, etc.* Copulation in the hermaphrodite Gastropods is 

 reciprocal. 



E 



Fig. 246. Diagram of the genitalia of various Gastropoda. Sexual gland in each case 

 dotted. A — C Proaobranohiata, A female, B and males ; D Opisthobran- 

 ohiata; JSOpisthobranohiata and Pulmonata. $ oviduct, ? ' female 

 genital aperture, g sperm duet, <? ' male genital opening, ^ hemaphrodite duct, p penis, 

 r seminal groove. — Orig. 



The terrestrial Pulmonata lay their eggs in the eai"th, each egg is stu-rounded 

 by a large mass of albumen which is covered by a more or less calcified, 

 round or oval, shell; the latter is very Uke that of a Bird's egg. In the fresh- 

 water Puhnonata each egg is similarly covered by a mass of albumen and a very 

 thin transparent outer shell, but a number of such eggs he in a common mass 

 of jelly (adheihig to plants, etc.) ; those of the Opisthobranchs, and of some of 

 the ProBobranchs, ai-e similai-ly arranged ; in most Prosobranchs {e.g., the Whelk), 

 however, several eggs lie without separate sheUs in a common mass of albumen, 

 which is sun-ounded by a leathery capsule; the capsules, which often adhere 

 together in groups, are of very diverse, and often strange shapes. Several of 



* In some terrestrial Pulmonata (e g., the common species of Heliie) there is a, 

 " d a r t - s a c ,'' an evagination of the oviduct close to the external genital aperture, 

 in which a calcareous body, somewhat of the form of an arrow, the " dart," is 

 secreted ; it is extruded during copulation, and is to be regarded as an excitatory 

 organ. 



