292 
Part III. -Eighth Annual Report 
In the waters of the Firth of Forth, the reproductive activity of the 
Scallops extends over a lengthened period of the year. At the end of 
February and beginning of March specimens were obtained with re- 
productive organs having the characteristic colour which the sexually 
mature forms exhibit. The number, however, in this condition in the early 
spring was not numerous ; but as the season advanced the proportion with 
ripe reproductive organs increased, till in July and August a maximum was 
reached. In those months almost all of the forms dredged from a parti- 
cular area were ripe, but as September w r as approached the specimens taken 
from the same area showed by the colour of their reproductive organs, and 
by the diminished size of these, that the period of spatting was drawing to 
a close. In this same area towards the middle of September hundreds 
might be examined without a single ripe specimen being found. During 
September, when ripe forms were desired, these were obtained from ground 
about a mile eastwards from the dredging ground of the previous months. 
This is interesting, as showing how, in the same species on neighbouring 
bottom, the spatting period may differ to the extent of a month or even 
two. As the season progressed, and in October, the condition of the 
generative organs showed that the sexual products had been shed. In 
the beginning of October it was still possible to obtain a few ripe forms, 
but not without examining large quantities taken by the dredge. 
On the whole, while reproductive activity was most marked in the 
summer months, the spatting period of P. opercularis on the Forth clam beds 
has a much wider range. In the summer of 1889 it reached its maximum 
in the beginning of August, and in September immense numbers of free 
swimming larval Lamellibranchs, which I took to be P. opercularis, were 
obtained by the tow-net worked at various heights above the beds. 
The method adopted in fertilising was to cut out the ovarial and seminal 
parts of the 1 tongues ' from a dozen ripe auimals into two glass vessels. The 
ovarial portions were separated roughly from the testicular, and minced 
fine, and then strained through very fine muslin into the vessel partially 
filled with clear sea-water. The spermatic portions were similarly dealt 
Avith, and the filtered contents of this vessel were added to the vessel 
containing the ova. The whole was stirred and allowed for some time to 
settle, when the supernatant water was decanted off, and afresh supply of 
sea water introduced. The changes of this water were frequent at first, but, 
notwithstanding, the death-rate was occasionally very large. More than 
once the brood was entirely destroyed ; especially if the fluid was allowed 
to stand for a few hours too long before being changed the death-rate was 
increased, and the decaying dead forms brought about the death of the 
remainder. One or tw T o difficulties were experienced which militated 
against successful hatching. One was the getting of sufficiently clean 
water for the small glass aquaria. Time after time the whole of the 
embryos were lost from the continuing accumulation of fine sediment that 
settled on the bottom of the aquaria in spite of the precautions taken to 
obtain clear w T ater, by filtering, a necessity in the absence of settling ponds. 
A substitute for these last was found in carrying the water from the 
hollows in the rocks situated between tide marks. These hollows acted as 
miniature settling ponds, and the water was carried about three hundred 
yards to the wooden sail-shed (part of which was placed at the writer's 
disposal), where the glass aquaria were. The dust at all times so abounded 
in the atmosphere of this temporary structure that it was extremely 
difficult to keep it from entering the aquaria, although these were covered 
to prevent the entrance of dust. 
When liberated artificially from the ovum the ovarian cells are more or 
less irregular in shape, being generally polyhedral and drawn out into a 
