270 MESSRS. C. SHEARER, W. DE MORGAN, AND H. M. PUCHS 



E. miliaris is subject to considerable variation in general shape (the test being 

 sometimes extremely depressed), in coloration, and in the length and stoutness of 

 the spines. In Plate 25, fig. 124, left hand, the usual form of E. miliaris from the 

 Plymouth district. The test is depressed, the spines are short and stumpy. The 

 colour is a dark green, with a certain amoixnt of violet at the tips of the spines. 

 Many examples, however, from the same grounds have spines which are longer, and 

 the general pigmentation may be lighter. In the same fig. 124 (right side) is also 

 shown a variety of E. miliaris obtained from Brixham. These urchins had long 

 and delicate spines, and the general coloration was a light green. There is a 

 considerable amount of variation between the two extremes shown in Plate 25, 

 fig. 124, but the Plymouth specimens are never so long-spined as those taken from 

 Brixham. Plate 25, fig. 125, is a reproduction of a life-size photograph of an 

 E. miliaris reared in the laboratory. It will be seen tliat it has long delicate 

 spines like the long-spined variety just described. All the E. miliaris raised in the 

 laboratory have been of this variety, although they were bred from the short- spined 

 variety found in Wembury Bay. This shows that these varieties of E. miliarts 

 are not distinct races, but are due to the conditions surrounding the individuals 

 during growth. 



The long-spined urchins from Brixham are very important for quite another 

 reason. They are the only Echinoids of which the age is definitely known. 



In 1910 a coal hulk liad been anchored off Brixham, Devonshire, her bottom 

 having been previously scraped and painted in dry dock in April, 1910. This vessel 

 was brought again to Plymouth on August 1, 1911, and had her bottom scraped ; 

 it was then found that there were large numbers of E. miliaris attached to her. 

 These were all of the long-spined variety described above, and they varied in 

 diameter from 3 to (> cm. across the spines. Almost all of these urchins were 

 mature ; and since they could only have attached themselves to the floating hulk 

 just before metamorphosis, they could not be more than a year old. We raised 

 a large number of hybrids and pure-bred urchins from this material. 



It will thus be seen that in the sea E. miliaris can mature and produce ripe germ 

 cells within the first year of its existence. In the laboratory we have been 

 successful also in getting our E. miliaris, raised from the egg, to produce ripe egg 

 cells when they were barely twelve months old. This has established the fact that 

 our laboratory conditions, after all, are not so unfavourable for this species, judging 

 from the fact that the urchins raised in captivity produced germ cells in about the 

 same time as those growing at large in the sea. 



It is remarkable that all three species (jf Echitivs that we have used in this work 

 can become sexually matuie when relatively small and much below their normal full 

 size. We have obtained ripe eggs from urchins of E. miliaris when these have 

 measured less than one centirhetre across the spines. In E. esculentus and E. acutus 

 we have likewise frequently found ripe females a mere fraction of their full size. 



