DEPARTMENT OF MARINE BIOLOGY. 193 



only by the ease with which specimens could be kept over night in small 

 aquaria, but by their ability to withstand a wide range of temperature and 

 an equally remarkable range of sahnity. They also showed an indifference 

 to bright light that was unexpected. The temperature range is well over 

 12° C; it was not feasible to determine the minimum temperature, but the 

 lowest observed was approximately 22°. Temperatures as high as 34° were 

 not fatal unless prolonged; the critical point seems to be between 35° and 

 36°. It is possible, of course, even if not probable, that temperatures much 

 below 22° would not be fatal. The sahnity range was determined both by 

 diluting normal sea-water with rain-water and by evaporation of sea-water at 

 laboratory temperature to the desired concentration. Individuals survived 

 12 hours in sea-water so dilute (75 to 80 per cent normal) that their color was 

 sGmewhat extracted, the water becoming distinctly yellow. On the other 

 hand, water 10 per cent more saline than normal produced no apparent injur- 

 ious effects in 12 hours, and 3 hours in water 20 per cent more saline than 

 normal was not fatal. 



A second line of work was connected wdth the accumulation of material to 

 show growth-changes in young echinoderms. After the completion of the 

 larval stage, which is usually passed swimming freely in the sea, most echino- 

 derms assume quickly the adult form, but are of very minute size. The 

 subsequent growth-changes throw a flood of light on phylogenetic history, but 

 relatively little has yet been done in working them out. At the Pigeon Point 

 laboratory I secured material showing more or less fully the growth-changes in 

 3 species of starfish, 9 species of brittle-stars, 1 sea-urchin, and 4 holothurians. 

 Of course, in most of these the series of developing individuals is incomplete, 

 but in at least three of the brittle-stars, one starfish, and one holothurian it is 

 sufficient to yield results of great importance. 



The third line of research was concerned with the composition of the echino- 

 derm fauna of Tobago. During the 5 weeks we collected 75 species, of which 

 about one-fifth seem to be new to science. Some of those which are not new 

 are of even greater interest, either because their habitat has not previously 

 been known or because their occurrence at Tobago is a notable extension of 

 their range. It is my purpose to make a critical study of this Tobagoan fauna 

 in comparison with that of Jamaica and the other West Indian islands, in the 

 belief that such a study will throw light on the past history of the Caribbean 

 region. It may be mentioned in passing that more than one-third of the 

 species of echinoderms found at Tobago are not yet known from Jamaica. 



On the Development of Some West Indian Echinoderms, hy Th. Mortensen. 



The time spent at the island of Tobago (March 23 to April 23) turned 

 out to be very profitable for studying the development of echinoderms, a 

 considerable percentage of the species being ripe at this season. The physical 

 conditions were also unusually good, the oceanic currents that sweep round 

 the island and the limestone formation of the south end of the island, where 

 the laboratory of the expedition was established, both being important fac- 

 tors for producing the pure water so essential for rearing echinoderm larvae. 

 This, together with the unusual richness of the littoral echinoderm fauna, again 

 the result of the physical conditions, accounts for the decided success the 

 writer's efforts met. Ten different forms were studied, as follows: 



Diadema antillarum Tripneustes esculentus Ophiothrix angulata, 



Echinometra lucunter Mellita 6-perforata var. nov. 



Ophionereis squamulosa Araphiura sp. nov.^ Ophidiaster guildingii 



Tropiometra carinata Lytechinus variegatus 



*I am indebted to Dr. H. L. Clark for the specific names of these ophiuroids. 



