34 THE NAUTILUS. 



From April 26 to 30, 1908, I was able to devote a short vacation 

 exclusively to a minute examination, as exhaustive as time permit- 

 ted, of the nudibranch life on two short stretches of coast suitable 

 for breeding Eolid nudibranchs. The first was a stretch of granite 

 ledges and piles of broken boulders at Rocky Neck, in Gloucester 

 Harbor; the second a stretch of granite ledges at Brace's Cove, on 

 the outer (eastern) side of Eastern Point, Gloucester, Mass. The 

 localities were quite unlike in biological character, though resembling 

 each other as shore formations. The Rocky Neck locality was 

 bathed by the comparatively warm and still waters of the harbor, 

 thick with larvae, eggs, spores and organic debris of all kinds. In- 

 numerable small and rather deep pools among the broken boulders, 

 thickly hung and often completely choked with fuci, sheltered 

 abundant animal life, including Metridium and hydroids. The 

 Brace's Cove locality was pounded by the eternal surf of the open 

 Atlantic, and the water was noticeably colder and crystal-clear. 

 The pools on the massive ledges were much larger, shallower and 

 more open. Corralines were abundant, hydroids and Metridium 

 much fewer. 



a Polycerid from Zanzibar, as follows: "* * * this form provided a most strik- 

 ing case of the migration of molluscs in flocks to shallow water for the deposi- 

 tion of spawn. But a few specimens were collected before a certain period of 

 a few days' duration, when the sand of Chuaka Bay just below low-tide mark 

 was occupied by astonishing numbers * * *. These were not washed up by 

 accident, but were all actively ciawling on the sand among the weeds, etc. 

 Many were in coitu, and when placed in basins of sea-water most of the speci- 

 mens were soon engaged in copulation or the deposition of yellow egg-ribbons. 

 By-and-by the swarm disappeared to some unknown permanent habitat. If 

 this were in the deeper channels of the bay (1 to 2 fathoms deep at low tide) 

 they must have been found there by dredging. As this was not the case 

 it seems most probable that the migrations of these tiny animals extend to and 

 from the deep sea three or more miles away." 



One may be permitted to guess that the "unknown permanent habitat" 

 to which "the swarm disappeared" was that bourne from which no traveler 

 returns ! Quite jjrobably the form may be found to be strictly annual with little 

 or no overlap of generations, as I believe is the case with various of our own 

 forms. Either the young escape observation till just about the breeding 

 season (possibly making a very sudden and rapid growth at that time which 

 may be marked by a change in food supply) or else, and more probably, the 

 young straggle back to deep water as they grow stronger, but while still small, 

 and, there attaining their growth, make a sudden descent (or ascent!) upon the 

 shore en masse at the next call of the breeding impulse. 



