NOTES AND MEMORANDA. 195 



same tank, under the same circumstances of illumination and environ- 

 ment, may be seen wrasse of several different liveries. 



The uncertainty of the nature of the stimulus is further borne 

 out by the observation of five small L. maculatus taken in the Yealm 

 zostera beds on the same date as the large one. 



These specimens measured from 2^ to 3 inches in length. During a 

 period of 48 hours they were transferred to different vessels in the 

 following order : — 



1. White porcelain pots sheltered from bright sunlight. 



2. Glass bell-jars similarly sheltered. 



3. A table-tank with black sides and bottom. 



(a) 3 inches long, uniform bright green on reaching the Laboratory, 

 unchanged in 1 and 2 ; escaped from 2 and died. 



(b) 3 inches long, uniform dark olive in 1, uniform but brighter and 

 greener in 2, duller with very faint bars in 3. 



(c) 3 inches long, uniform pale olive in 1, uniform buff in 2. 



(d) 2f inches long, uniform pale olive in 1, uniform darker olive 

 in 2. 



(e) 21 inches long, uniform pale olive in 1, slightly darker olive with 

 faint bars in 2. 



c, d, and e all assumed in 3 the ordinary olive ground colour with 

 faint bars. E. W. L. H. and L. W. B. 



The Incubation of the Skate-leech. 



Pontobdella muricata. Linn. 



The ova of the skate-leech are probably familiar to most marine 

 zoologists, and, apart from any literature on the subject, can 

 almost always be recognised by the presence of the parent. The 

 shell is hard and chitinous, of an olive-brown colour. It is almost 

 spherical, about 4 to 5 mm. in diameter, and attached by tlie flattened 

 base of a short peduncle to the object selected by the parent. On 

 either side of the spherical part of the shell is a rounded fenestra, of 

 which one at least is simply closed by dark membranous matter. The 

 chitinous matter of the other appears to be, at all events occasionally, 

 imperforate. The ova are deposited separately, but for the most part 

 close to each other, either on an old shell or on some other convenient 

 object. 



On the 31st July, 1897, about four miles W.S.W. of the Plymouth 

 Mewstone, the trawl brought up a large and fairly recent scallop shell, 

 Peden maximus, the valves still united by the hinge. Inside was a 

 skate-leech mounting guard over a group of eggs attached to the flat 



