~ JUNE 30, 1 on 
in the living state. The records made at 
laboratory down to 1919 showed that E. miliaris has | 
been found to breed from about February-March to 
August. In 1920 I arrived at the conclusion: that 
certain marine animals, such as the oyster, breed 
continuously so long as the sea-temperature remains 
above a definite temperature, providing the general 
biological conditions are otherwise normal. én this 
view, and if the of breeding in E. miliaris were 
the same as that of the oyster, the breeding period of 
this sea-urchin should be found to extend to about 
November-December, on the average. 
In March and April 1920 many successful artificial 
fertilisations of E. miliaris were made, and it may be 
assumed that similar successful fertilisations could 
have been obtained onwards to August. After 
August periodical collections of this urchin were made 
from the shore to test the view mentioned above. On 
o Samaepge 14 the proportion of ripe individuals 
collected was high and six excellent artificial fertilisa- 
tions made; on October 13 the proportion of ripe 
individuals collected was smaller, but good fertilisa- 
tions were still obtained, and on October 29, although 
the proportion of ripe individuals was now lower, an 
optimum fertilisation was obtained yielding very 
fine and healthy pluteion November 1. The observa- 
tions at Plymouth were interrupted at this time, but 
on November 3 a high proportion of E. miliaris which 
had been dredged from the oyster beds off Whitstable 
were found to be ripe and yielded healthy larve, which 
lived in some bowls as plutei until at least January 5, 
1921. A batch of similar urchins forwarded to 
Plymouth yielded an excellent fertilisation on Novem- 
ber 10,1 and although no fertilisation was made later, 
it was observed at various times during the winter 
that the gonads of Whitstable specimens examined 
remained full. A sample of urchins examined at 
Plymouth on January 26, 1921, showed that a small 
proportion of ripe males with full gonads still occurred 
but no ripe female was found, and the big variation 
in size of the gonad observed in the remainder of this 
sample points to a distinct physiological difference 
between the Plymouth and Whitstable groups. 
It is thus clear that successful artificial fertilisations 
of E. miliayis may be obtained from Plymouth 
specimens during about the period February-March 
to November, and that the breeding period in the 
south of England may be considered to extend 
over the same range, but it is nevertheless open 
to doubt whether the capacity to yield a successful 
fertilisation may be good evidence that a species is 
breeding. 
The fact that breeding individuals may be obtained 
over such a long period of the year affords good 
reason to believe that single individuals may spawn 
several times a year, but there is no evidence that 
collective TaN occurs in this species at one 
given phase of the lunar cycle such as Fox found to 
be the case in the Mediterranean sea-urchin Diadema 
setasum (see NATURE, February 23, 1922). In three 
collections of E. miliaris from Looe Is. near Plymouth, 
on September 23, October 12, and October 28 respec- 
tively, the unripe individuals showed variation in the 
size of the gonad ranging from about 1/12 to a full 
gonad. These observations do not, however, rule out 
the possibility of spawning occurring normally—in 
those individuals which are ripe—at certain definite 
phases of the lunar cycle, for example, after any low- 
water springs; for it has been observed not in- 
1 This fertilisation and the one at Plymouth on October 29 were made 
by Mr. A. J. Smith. The larve from the Whitstable urchins November 
and the Plymouth ones October 29, showed a fine apical tuft of cilia, whi 
appears not to have been 
described a similar tuft in E. esculentus. 
No. 2800, VOL. 111] 
NATURE 
of fertilisation, segmentation and gastrulation stages 
in E. miliaris, although MacBride has |» 
879 
frequently that ripe specimens collected at low-water 
spawn before arriving at the laboratory. 
The sex-conditions in the collection of E. miliaris 
mentioned above were examined closely for any 
appearances indicating sex-change ; for a condition 
of sex-change in sea-urchins may be regarded as a 

_ possibility in view of Mortensen’s discovery of the 
common occurrence of protandric hermaphroditism 
in ophiuroids and of Fox’s observation referred to 
-above but not known at that time of the very rapid 
(monthly) filling and emptying of the gonads in the 
sea-urchin, Diadema: it is also worthy of note that 
Gray (Proc. Camb. Phil. Soc., xx. pt. 4, 1921) has 
described isolated cases of apparent and true herma- 
phroditism in the sea-urchins Arbacia and Stron- 
gylocentrotus. In Echinus miliaris, however, no 
definite hermaphrodites were found, but in several 
gonads at about the period of change from the spent 
condition to the rematuring stage, a small quantity 
of sperm was found together with gonocytes appar- 
ently too large for spermatocytes, and gonads were 
found having a colour generally associated with one 
sex but with young sex-elements of the other sex. 
The female gonad in E. miliaris varies in colour from 
white when young to yellow or orange when mature, 
whereas the male gonad -varies from brown to grey. 
These differences of colour are undoubtedly an out- 
ward expression of the differences in metabolism in 
the sexes leading up to—or consequent upon—the 
production of mature sex-elements. 
A similar sexual colour difference is observable in 
the gonad of other animals ; for example, in Crepidula 
fornicata the gonad in the male stage is brownish red 
but yellow in the female, while that of the herma- 
phrodite stage is orange, and it has already been 
shown (Orton, Proc. Roy. Soc., vol. 81, B, 1909) that 
in the case of Crepidula the primary sexual characters 
precede in development and forecast the appearance 
of the secondary sexual characters. Thus the colour 
of the gonad in animals is undoubtedly closely con- 
nected with deep-seated changes—probably induced 
by sex-hormones or, as Geoffrey Smith visualised 
them, sexual formative substances—which are 
different for the mature male and female condition, 
and apparently also for a potential condition of sex 
while sex is yet unrecognisable in the primary sex- 
elements. 
It would, therefore, seem possible that a chemical 
test might be devised to detect a sex-potentiality in 
an undifferentiated gonad. Such a test if obtained 
would be a very valuable help in investigating 
suspected cases of sex-change, especially in cases 
where a change-over of sex may occur between 
successive periods of growth of the gonad as is 
possible in ns miliaris, Mytilus edulis, and other 
animals, but more probable in the case of the common 
limpet, Patella vulgata. In this kind of sex-change 
the residual sex-elements in a gonad would often give 
a clue to the recent sex-condition, while the chemical 
test would provide evidence of the forthcoming or 
potential sex-condition. 
The rapid change-over of sex in the oyster is also 
very strongly suggestive of the existence of a sex- 
hormone, as the gonad in a female-functioning oyster 
normally changes over quite suddenly after the 
extrusion of the ripe ova to the production of male 
elements only. There is good ground, therefore, for 
looking for a chemical test for sex-potentiality, 
especially in invertebrates, and there is no doubt 
that our knowledge of sex-conditions would increase 
rapidly after the discovery of such a test. 
J. H. Orton. 
Marine Biological Laboratory, 
Plymouth, May 24. 
