38 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I28 



eggs — from 753 to 761 microns in diameter — were found in several 

 individuals. These eggs were largely yolk. 



Brooding of eggs was practiced by the tunicates also. On October 

 6, 1949, a specimen of Dendrodoa grossularia was found in which 

 the atrial cavity was filled with eggs of a large size. 



The production of large eggs by Arctic marine invertebrates is 

 essential to brooding, for if the embryo is to develop to the crawling 

 or other advanced stage before hatching, it must be supplied with a 

 large yolk for growth. 



Among the most surprising of these large eggs were those of the 

 echiuroid worm Hamingia arctica, which were 900 microns in diame- 

 ter and which perhaps accounted for the unusually large trochophore 

 larvae that were occasionally found in the plankton. 



Although the eggs of Eukrohnia haniata were not seen, they must, 

 in order to produce embryos that were 3 mm. in length, have been 

 large for a chaetognath. The same deduction can be made for the 

 eggs of the leech mentioned above. 



Several of the polychaete worms produce large yolky eggs, e. g., 

 Antolytus jallax. A. alexandri, Sphaerosyllis erinaceus, Exogone 

 naidina, Ensyllis blomstrandi, Capitella capitata, Nicolea venustula, 

 Lanassa venusta, Polycirrus medusa, and Potamilla neglecta. 



Many of the amphipods have exceptionally large eggs for the size 

 of the animal. For instance, females of Unciola leucopis only 12.5 to 

 14 mm. in length produce eggs that are 0.7 mm. in diameter and from 

 which emerge larvae 2.7 mm. in length; and PJiotis reinhardti, with 

 females from 4.5 to 5 mm. in length, has eggs 0.5 mm. in diameter. 

 In Ischyrocerus commensalis one female 3 mm. long was carrying 3 

 eggs 0.3 mm. in diameter, and another 5 mm. long was carrying 15 

 eggs that were nearly 0.5 mm. in diameter ; in Eurystheus melanops 

 females from 3.5 to 8 mm. long were carrying from 3 to 10 eggs from 

 0.4 to 0.5 mm. in diameter. 



The eggs of the clam Musculus cornigatus measuring about 500 

 microns in diameter, and of the clam Cardita crassidcns measuring 

 from 753 to 761 microns in diameter, have been mentioned above. 



In the gastropods large embryos may result from the production 

 of large eggs or from the production of a large number of small 

 eggs in which only a few hatch into embryos that feed on the unde- 

 veloped eggs. In still other instances eggs are provided with a nutri- 

 tive substance similar to egg white upon which the developing em- 

 bryos feed. Some of the species produce large eggs that are retained, 

 probably within the pallial cavity, until the embryos are in the crawling 



