38 



hesitate in identifying it with this species. The only difference noticeable 

 is this that the postoral and postero-dorsal rods are somewhat more 

 closely thorny than was the case in the reared larvae. (Of course, there 

 is a possibility that this larva may really belong to one of the other species 

 of Lytechinus occurring in the West Indies, viz. L. euerces H. L. Clark, 

 L. dyscritus H. L. Clark and L. callipeplus H. L. Clark.) The larva is not 

 sufficiently well preserved for showing the body shape distinctly. — In 

 PI. Ill, Fig. 2 a small rod is seen lying across the posterior transverse 

 rod in the midline. This is, however, a separate rod, which, I suppose, 

 represents the first rudiment of the Echinoid skeleton. The postero-dorsal 

 rod is simple like the postoral rod. The dorsal arch is characteristic in 

 having a pair of lateral processes, which support the lobe formed by the 

 dorsal lateral band. 



The postoral and postero-dorsal arms are generally upwards directed, 

 but they are movable and may be directed nearly horizontally. 



Lytechinus anatnesus H. L. Clark. 



PI. VII, Fig. 5; PI. VIII, Figs. 3—1. 



During the stay at the Biological Station at La Jolla, Cal., in August- 

 September 1915 I had the opportunity of undertaking a fertihzation of 

 this species, which occurs in great numbers off the Californian coast in 

 depths of ca. 40—250 meters. The fertilization was made on the 24th of 

 August on board the ship, immediately after the dredging, and was very 

 successful. 



The eggs are small (I have no measurement of them) and perfectly 

 clear — a most excellent object for embryological studies. After 20 hours 

 there were swimming blastulse (probably earlier), and after 24 hours 

 the gastrula stage was reached. The formation of the skeleton began 

 when the embryos were 2 days old. At the age of 7 days the postero- 

 dorsal arms had begun to develop, with the skeletal rod, and also the 

 preoral arms had appeared; the dorsal arch had just begun to form at the 

 same time, its branches being still far from the preoral arms (PI. VIII, 

 Fig. 4), which are thus from the beginning formed independently of the 

 rods which later on grow to support them, while otherwise the rule would 

 appear to be that the supporting rods are so to say pushing out the arms 

 At the age of 11 days four epaulets had developed, and the absorption 

 of the body skeleton had begun. 



..^Il^ J'7 ^^^ ""^ *^^ ^^'""^ ''''^'''^'^ ^^'' «tage. On leaving La Jolla 

 the 17th September I carried the culture along with me to San Pedro 



ir'J!.^^'^ ""^ °PP«^t^"ity of paying further attention to it until the 

 26th. There was then found to be only one fully developed larva which 



