202 



Part III. — Sixteenth Annual Report 



records of these three stations is that for Station IV. This difference in 

 the numbers of the records of these young forms is satisfactorily explained 

 by the fact that the greater number of the Barnacle tribe, in our seas at 

 least, are to be found attached to rocks, stones, and other objects inshore, 

 and that there the young are usually to be found. 



Formula (2) shows the total number of records of young Balani for 

 each of the twelve months for all of the six stations : — 



It is evident from the numbers in this formula that the Balani hatch 

 out principally in April, and that after April there is a rapid diminution 

 in the production of larval forms, after which a more or less complete 

 cessation takes place, there being not a single record for all the six 

 months from September to February. 



Formula (3) shows the total number of records of young Balani for 

 each of the seven years for all the six stations : — 



Numbersof the Years. . - . . 1889. 1890. 1891. 1892. 1893. 1894. 1895. 

 Total number of Records for each Year, -4 9 20 7 11 5 2 



The number of records for 1891 is greatly in excess of that for any of 

 the other seven years, but 'the reason for this marked difference does 

 not seem to be very clear. 



But the records of young Schizopoda and Balani form a comparatively 

 small part of the whole number. The largest proportion of the three 

 hundred and forty records of young and larval Crustacea are those of 

 various species of Decapods, as has already been stated. But resuming 

 consideration of the young Crustacea, we find by an examination of the 

 general Table of Distribution that with one exception there are no records 

 for January and February in all the seven years and for all the stations. 

 After this a sudden increase is observed over all the stations, so much so 

 that in regard to two of the stations the maximnm of records is reached 

 in April. From this time the number decreases somewhat till August, 

 when a marked extension occurs over all the stations, the number after- 

 ward gradually diminishing till November. In December there is a 

 somewhat sudden drop to one or two records, or, in the case of two of the 

 stations, to none at all. This sudden increase and subsequent continuance 

 of the moderately high numbers of the monthly records till November is 

 an indication that in March and April an extensive and more or less simul- 

 taneous hatching of Crustacean ova takes place, and that it continues 

 more or less all through the summer and autumn and on till about the 

 end of the year. Of course it is not suggested that it is the same species 

 that produces these young forms all the year through, but that the ova 

 of different species hatch out at different seasons and thus keep up the 

 supply of larval and young forms. The subjoined formulae, prepared from 

 the numbers in the Table of Distribution, show more clearly by the 

 arrangement of the numbers in this way some of the special features 

 referred to in the distribution of the young and larval Crustacea. 



Formula (1) shows the total number of the records of young Crus- 

 tacea for each of the six stations, which are divided into inner and outer 

 stations :— 



Total number of Records for each Month, 



Names of the Months, 



Number of the Stations, - . . . 

 Total number of Records for each Station , - 



Inner Stations. 

 I. III. IV. 



70 60 55 



Outer Stations. 

 V. VIII. IX. 



56 49 50 



