324 J, H. ORTON. 



G. ficta was the dominant Nudibranch, and 53 specimens were brought in 

 and measured. Their average length from tip of head to end of tail was 11 

 mms., and they varied in length from 7 to 17 mms. Masses of spawn of 

 both G. picta and exigua were present on the hydroids, and from these 

 masses free-swimming veligers were being given off. Thus these Nudi- 

 branchs had undoubtedly peopled the raft as veligers, rushed through 

 theirdevelopment atthe expense of the hydroid,and were giving off veligers 

 againto populate hydroids elsewhere within a period notlonger thanGweeks 

 and 2 days. Such a rapid growth is very probably a necessity for hydroid- 

 feeding organisms, since the hydroids themselves attain maturity very 

 quickly. In this respect it is also of great importance to the race that 

 some Nudibranchs are protandric hermaphrodites,* for by this means a 

 few individuals are able to multiply rapidly where food is abundant, and 

 thus the race by means of its free-swimming larvae is frequently able to 

 utilize an abundant food-supply wherever such is available. 



THE LIFE-HISTORY OF CIONA, CLAVELLINA, AND 

 ASCIDIELLA. 



In the group of Tunicata the rate of growth in many species has been 

 thoroughly worked out. Ciona intestinalis, Ascidiella aspersa, Molgula 

 ampulloides ? have all been found to be ripe and yield embryos on being 

 artificially fertilized at an age of not more than 2>\ months, and in some 

 cases have themselves extruded fertilized eggs. Better fertilizations 

 of these forms are, however, obtained from specimens about 4j- 

 months old. At an age of less than 15 weeks Ascidia conchilega 

 from the Essex coast also gave 100 per cent of tadpoles on being 

 artificially fertilized. Large numbers of successful artificial fertilizations 

 were made in this group in running down the minimum age at which 

 tadpoles can be obtained, and it was generally noticed that cross- 

 fertilizations gave better results than self-fertilizations. All these 

 species, however, grow at a much greater rate in the summer and autumn 

 than at any other time of the year, and in the months of August and 

 September ClaveUina lepadifonnis and Leptoclinum {Diplosoma) gelati- 

 nosum grew from the tadpole to a tadpole-bearing adult within 8 weeks. 

 In one remarkable case L. gelatinosum was found to have raced through 

 the whole life-cycle from the tadpole to an adult form giving off tadpoles at 

 an age not greater than 3 weeks and 5 days. And indeed about this time 

 of the year, August, this compound Ascidian is to be found overgrowing 

 almost everything, both about and below low-water mark. 



* As has been found by the writer in researches in this group. 



