NO, 9 MARINE INVERTEBRATES, ALASKA MacGINITIE yj 



that produce embryos requiring a relatively long pelagic life. Growth 

 of nonpelagic embryos to an advanced stage is accomplished by the 

 production of large eggs, or eggs from which the embryos develop 

 within the mother, or by the feeding of embryos on nurse eggs or on a 

 nutritive white material. 



Capsules and masses of jelly containing snail eggs were abundant 

 and varied at Point Barrow. Few gastropod larvae were observed in 

 the plankton. Most of the data collected on the breeding season of 

 the gastropods are contained in table 4 (p. 41). 



At Point Barrow other invertebrates besides snails brood their 

 eggs. The large chaetognath Eukrohnia hamata was observed brood- 

 ing its eggs until the young were 3 mm. in length. No other instance 

 of the brooding of eggs has been reported in this group of animals. 



Several of the polychaete worms carry their eggs or incubate them 

 in some manner, Autolytus fallax carries its eggs ventrally in an 

 egg sac (usually one, sometimes two), and A. alexandri, according 

 to Wesenberg-Lund (1947), carries its eggs ventrally in two egg sacs. 

 Sphaerosyllis erinaceus carries its eggs attached to its dorsal surface 

 between the neuropodia and dorsal cirri (i to 4 eggs per segment 

 on setigers 8 to 24). Exogone naidina carries its eggs attached to its 

 ventral surface on about 7 to 14 segments (usually 4 per segment, but 

 sometimes i to 3 per segment). In all four of these worms the eggs 

 are retained until they hatch into young worms. Potamilla neglecta 

 deposits its eggs on the inner surface of its tube, about one-third of 

 the way down, and then secretes a thin, transparent membrane be- 

 tween itself and its eggs. Spirorbis gramdatus incubates its eggs in 

 a large brood pouch in the operculum, and ^. spirillum incubates its 

 eggs within its tube. 



The leech Crangonobdella murmanica lays a large egg in a capsule 

 that is attached singly to the host. The egg develops into a young 

 worm before hatching. 



The clam Musciilus corrugatus lays large eggs within the byssal 

 capsule with which it surrounds itself prior to spawning. The eggs 

 remain inside the capsule until they develop into young clams. Al- 

 though no individuals of M. laevigatus were found with eggs within 

 their capsules of byssus threads, it is obvious that this clam also re- 

 tains its eggs, for none of the younger specimens were within a net, 

 or capsule, whereas individuals 20 mm. or more in length that were 

 surrounded by such a byssal net were not uncommon. 



It also appears probable that the clam Cardita crassidens has some 

 arrangement for caring for its eggs, probably retaining them within 

 the mantle cavity until young clams are formed, for unusually large 



