224: TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



REPORT ON THE PERIODIC SAMPLES OF SHRIMPS 

 FROM THE MERSEY ESTUARY. 



By T. Monaghan. 



Assistant Naturalist in the Fisheries Laboratory. 



These investigations were first carried out during 1912 

 and part of 1913, but a definite result could not be obtained 

 on account of the insufficiency and irregularity of the samples 

 sent to the laboratory. The result of the observations for 

 1912-13 were published in the Annual Report for 1913. This 

 year the samples have been sent in with greater regularity 

 so that the observations are more complete. 



The samples were taken from the Rock Channel and 

 Crosby Channel, both of which may be included in the term 

 " Mersey Estuary." It will be noticed from the data (Table I) 

 that, with a few exceptions, two samples were sent for examina- 

 tion each month, thus enabling me to compare the variation 

 in numbers of the sexes more closely than in 1913. As each 

 sample was sent the shrimps were first sorted out in their 

 sexes and then counted. They were measured (from the 

 tips of the antennules to the extreme end of the tail) in 

 millimetres, and averages were determined for each group. 

 At the same time a microscopic examination was made of 

 the eggs on the berried females, and four different stages 

 of development were recorded, viz. : — (1) Segmentation com- 

 mencing. (2) The eye forming. (3) Eye fully developed and 

 the appendages just showing. (4) Yellow and black pigment 

 formed, the larvae ready to hatch. A number of eggs in each 

 stage were then measured. These results are, however, not 

 yet completed, and are consequently not given in this Report. 



Table I shows the data as to samples obtained, and the 

 average lengths of the berried females, non-berried females 

 and males in each sample. 



Table II gives the percentages of berried females, non- 

 berried females and males for each month. 



