8 THE PHYSIOLOGY OF REPRODUCTION 



Some interesting observations have been recorded by Ashworth 

 and Annandale ^ about the breeding habits of sea-anemones. The 

 species Sagartia troglodytes and Actinia mesembryanthemum, which 

 are very prolific in captivity, have been noticed to breed regularly 

 in the early spring. Actinia commences to produce young in the 

 beginning of February, and Sagartia about a month later. As a rule 

 the young are extruded in the early morning, and one individual 

 may repeat the process every morning for a number of weeks, 

 when the breeding season comes to an end. In one season, when 

 the aquaria were somewhat neglected, . the specimens of Sagartia 

 produced fewer youUg than usual, and these were not extruded 

 until the beginning of April. Specimens of Actinia living in the 

 same aquaria were more prolific, but their breeding season was also 

 somewhat retarded. In the month of August two aneniones of the 

 species Sagartia troglodytes were brought from Thorshavn in the 

 Fferoes, and placed in the aqtiaria. In the following October both 

 of these produced several young; while in April of the. next year 

 one of them again gave birth, but only to a single anemone. It 

 seems probable that in this case the change of temperature or 

 environment had induced the anemones to breed at an unusual 

 season ; for it is unlikely that October is the normal period for 

 reproduction in the Fseroes, as by this time the sea has already 

 begun to run high, and there would be a great risk of the young 

 anemones becoming destroyed, being unable to attach themselves. 



Ashworth has pointed out^ that in the coral Xenia hicksoni, 

 which lives in the tropics, there is every evidence that spermatozoa 

 are discharged over a very considerable period, if not practically 

 throughout the whole year, whereas in the related form Alcyonium 

 digitatum, of Northern Europe, the period dijring which the sper- 

 matozoa are discharged is limited to about a month in the winter. 

 Ashworth remarks that the difference is probably due to the fact 

 that Xenia, living on reefs in the shallow waters of tropical seas, is 

 not subject to great variations jn temperature and food-supply, while 

 with Alcyonium such variations are no doubt considerable. In a 

 similar way Miss Pratt,^ who has studied the process of oogenesis in 

 Sarcophytum, Holophytum, and Selerophytwm, concludes that the 

 sexually mature condition in these tropical genera extends over a 



and' suggestive information on the factors which control breeding in plants 

 G. Klebs' work should be consulted. {Willhurliche Entmckelwngsanderunge'n 

 beiPflanzen, 1903.) 



1 Ashworth and Annandale, "Observations on some Aged Specimens of 

 Sagartia troglodytes, and on the Duration of Life in Coelenterates," Proc. Roy. 

 Soc. Edin., vol. xxv., 1904. 



^ Ashworth, "Structure of Xenia hicJcsoni," Quar. Jour. Micr. Science, 

 vol. xlii. 



2 Pratt, " On Some Alcyonidss," Herdman's Geylon Reports, vol. iii. 



