102 (.ASTROPODA. 



surrounded by a transparent membrane. In certain marine Gastro- 

 poda, e.g., in various Opisthobranchia, tbis gelatinous spawn attains 

 a great size, forming long, ribbon-like coils (Aeolis) or round cords 

 repeatedly bent back on themselves (Aplysia). In these cords, the 

 eggs either lie irregularly or else are arranged in one or more rows. 

 The mass of spawn often takes the form of a ribbon which is spirally 

 coiled (Doris, Doto, Pleurobranchus, etc.). These gelatinous masses 

 frequently contain a very large number of eggs, the spawn of a single 

 Doris having been estimated to contain 600,000 eggs. The spawn 

 sometimes has the form of a gelatinous sac attached to the substratum 

 by a stalk and containing thirty to forty eggs (Ten/ijjp*, according to 

 Salenka, No. 114). 



The eggs of the Heteropoda are also laid in gelatinous masses 

 which take the form of long ropes (Carinaria, Pterotrachea, Firo- 

 loida) according to Fol (No. 31); only the Atlantidae {Atlanta, 

 Oxygyrus) seem to lay their eggs singly, each surrounded by a 

 gelatinous envelope. The eggs of the Pteropoda also are found in 

 gelatinous masses which are usually tubular in sbape. These tubes 

 contain a great number of eggs placed either one behind the other 

 or else close together. The spawn less frequently appears in the 

 form of a thin membranous plate (Ore-ins aciculata), or as round 

 balls containing a large number of eggs (Olione).* 



In Fissurelln also the spawn forms a gelatinous mass containing a 

 large number of eggs and deposited on stones. The Prosobranchia for 

 the most part differ greatly from the above in their method of 

 oviposition. A variable number of eggs are usually enclosed in an 

 egg-capsule, the shape of which varies in different forms. Besides 

 the eggs, this capsule contains a fluid or viscid substance which 

 serves as nourishment to the embryo. We are hereby reminded of 

 the Oligochaeta and Hirudinea (Guat/iobdellidae) in the cocoons of 

 which several embryos are found floating in a nutritive fluid (Vol. i., 

 pp. 281 and -'591). The comparison becomes all the more striking 

 when we find that in a few Prosobranchs, as in the Oligochaeta (p. 

 281), not all the eggs in a capsule develop, but a few, or it may be 

 a large number disintegrate, and serve as food for those that survive. 

 In many Prosobranchia, however, all the eggs in a capsule develop, 

 in Fulgur, from 12 to 14, in Nassa, from 5 to 15, etc. In Purpura 

 floridana, the capsules contain many eggs, all of which undergo 



* Detailed statements as to the oviposition in the Pteropoda and also in the 

 Heteropoda are found in the works of Fol (Nos. 31 and 32). 



