97 



have no opportunity of changing the water, being at that time on a visit 

 in the interior of the country. Only a bottle of water was carried along 

 for removing the young embryos from the water in which the fertihzation 

 was made, which would, of course, be necessary, if there should be any 

 prospect of keeping the embryos alive for more than a very short time. 

 In spite of these unfavourable conditions the experiment proved quite 

 successful, the larvae developing quite normally until nearly full size. The 

 character of the egg could, of course, not be ascertained, so that I have 

 to leave undecided the question, whether it is surrounded by a mucilaginous 

 coat as appears otherwise to be the rule among Clypeastroids. Also the 

 cleavage could not be observed. Swimming gastrulse were found after 16 

 hours, and at 27 hours the postoral processes had begun to form. At the age 

 of 272 days the posterodorsal arms began to appear; the first indication 

 of metamorphosis — the formation of the amnion — was found in the 

 larvae when 372 days old. Beyond this stage the larvae did not develop, 

 excepting a slight prolongation of the arms, although they lived appar- 

 ently in full health for more than two weeks. No doubt, the lack of food 

 was the reason for their failing to develop further. Evidently, it must be 

 very easy to rear this larva through metamorphosis under suitable labora- 

 tory conditions. 



The shape of the larva (PI. X, Fig. 7) is that typical of Clypeastroid 

 larvse, the body only being slightly longer than usual. The arms are ap- 

 parently not widened ; their length in the fully formed larvae will probably 

 be found to be somewhat larger than shown in the figure, it is especially 

 to be expected that the posterodorsal and the preoral arms will be longer. 

 There is no indication of the formation of vibratile lobes. No pigment 

 spot in the points of the arms ( — so far as could be ascertained without 

 microscopical examination — ). — In the interior structure there are some 

 unusual features. The esophagus shows a clear space in its lower part, 

 apparently representing a kind of gizzard — a structure otherwise un- 

 known in Echinoderm larvae. The stomach has a rather characteristic, 

 nearly rectangular shape, which may, of course, be due to contraction on 

 preservation; but as such shape is not found in other preserved Echino- 

 derm larvae, it appears rather to be due to some special structure. From 

 its lower corners a string of cells is seen to proceed towards the ectoderm, 

 like a pair of strands by which the stomach is suspended in the very 

 spacious body cavity, which it is very far from filling out. To this band 

 the angular shape of the stomach would appear to be due, it being prevented 

 from contracting on the point where the string is attached. The hydrocoel 

 has not yet begun to form lobes. A hydropore canal is fairly distinct, 

 opening apparently in the midline on the dorsal side; the opening has, 



13 



