THE RELATIONSHIPS OF THE SEA-SPIDERS. 1 45 



body, beginning at the anterior end of the proboscis 

 and ending at the tip of the abdomen. As it passes 

 through the body it sends out long diverticulae into 

 the appendages — the mandibles and the legs — and an 

 anteriorly directed pair into the base of the proboscis. 

 These diverticulae are the most characteristic and in- 

 teresting structures in the group. 



The reproductive organs likewise extend from the 

 body into the walking-legs, and have their openings 

 on the second (proximal) joints of these appendages. 

 There is a simple tubular heart lying dorsal to the 

 intestine, which receives the blood through lateral ostia 

 to pump it over the body. 



These are the more important structures of the 

 Pycnogonids, or at any rate those which we will need 

 in our comparisons. 



The gallantry of the males must not pass unnoticed. 

 Each during the breeding season carries on its ovigerous 

 legs the developing eggs, which have been received, as 

 soon as laid, from the females. Curiously enough this 

 fact led naturalists into a most amusing blunder, inas- 

 much as it was tacitly assumed that those individuals 

 which took charge of the young and eggs must be the 

 females, and were described as such. 



The problem, and possibly its solution, which I wish 

 to present to-night, is the relationship of the Pycno- 

 gonids to other groups ; and the point of attack is to be 

 largely from the side of the embryology of the group. 

 There have been endless speculations as to the position 

 — zoologically — of these animals, but until within re- 

 cent years little was known of their anatomy, and prac- 

 tically nothing of their embryology. 



