488 TRANSACTIONS LIVEEPOOL BIOLOGICAL SOCIETY. 



pelagic specimen of this species which was obtained by 

 means of a weighted tow-net from near the bottom of 

 Port Erin Bay. The rudiments of four of the plates of the 

 apical system of the adult test are seen bearing the many- 

 pointed spines and sessile pedicellariae. The two larger 

 plates have formed around the proximal ends of two of 

 the skeletal rods which supported the arms of the pluteus. 

 MacBride (10) says that this strongly convex aboral sur- 

 face of the just metamorphosed Echinus becomes the 

 periproct of the adult. 



Fig. 58, PL IX, agrees so exactly in essential 

 details with Mortensen's (12) figure of the echino- 

 pluteus of Echinocardium cordatum that I have little 

 hesitation in referring to that species a larva which 

 occurred in considerable numbers in the plankton in July 

 and August, 1907, and in smaller numbers in the same 

 months of 1908.* In spite of careful scrutiny of the 

 official tow-nettings, taken twice weekly throughout the 

 year, it was not until September, 1913, that I noted its 

 reappearance in very small numbers. In 1907 and 1908, 

 the stages of metamorphosis, during the progress of which 

 a large quantity of deep purple pigment was developed 

 in the body of the larva, were abundantly represented; 

 and by using a weighted tow-net a number of post-larvae 

 were obtained from near the sandy bottom of the bay, 

 one of which is shown in fig. 59. At this stage the five 

 primary tube-feet are functional, and by their means the 

 tiny animals were observed to creep slowly over the bottom 

 of the vessel in which they were kept under observation. 

 But perhaps the most interesting feature of this post- 

 larva is the presence of five sphaeridia, each one closely 



* MacBride has recently published in the Quart. Journ. Micr. Science, 

 Vol. 59, Part 4, Feb., 1914, an account of the external features of the 

 development of Echinocardium cordatum. 



