23 



lion was undertaken repeatedly, none of the cultures proved very suc- 

 cessful, evidently on account of the water being not of sufficiently good 

 quality. The youngest stages were excellent, but as soon as Hie formation 

 of the Pluleus was about lo begin, the larva? became abnormal and died. 



The eggs are very small I regret lo have omitted to notice the exact 

 si/A' -- and very transparent. The developing embryos are most beauliful 

 objects, the cells are large and very clear, and the cell limils are very 

 distinct. 6 hours al'ler ferlili/alion they were swimming blasluhe; about 

 20 hours after ferlili/alion I he gastrula slage was reached. 



The young larva is a very curious objecl, ralher unlike olher young 

 Echinoderm larva 1 . II has the shape of a biconvex lens, wilh a perfectly 

 circular band, and recalls, in fad, a Trochophora by ils shape (PI. V 

 Fig. 1), while it is, of course, quile dilTerenl from a Trochophora in ils 

 analomical structure. The digestive organs are very small, the inoulh 

 opening being on the upper, the anal opening on the lower side. 



This stage was reached in three dilTerenl cultures, and there is no 

 reason to doubt that this is the normal shape of the young larva. II was 

 only after this stage was reached lhal the cultures went wrong. Only 

 in one case I succeeded in gelling them a little farther in Iheir develop- 

 ment. In PL V Fig. 2 is figured a young Pluleus which is, lo all appear- 

 ance, normal. II is no less peculiar than the younger slage. The postoral 

 arms are quite horizontal. (In the specimen drawn. Ihe only good 

 specimen available Ihe lefl arm is slightly upwards directed. It 



has been corrected in Ihe figure lo suil the right arm, which is quile 

 horizontal and has all the appearance of having preserved ils ualural 

 form and direction, while the olher has more the appearance of being 

 slightly distorted. However, since the skeleton is dissolved, it is impos- 

 sible to ascertain definitely which is the correct form of Ihe arms and 

 I have omitted lo notice anylhing aboul il from the living specimens.) 

 Olher processes are nol yd indicated; there is only an elevation indicating 

 Ihe oral and anal lobe. This larva is (> days old. The skeleton was begin- 

 ning to form al the age of Ihree days. Unfortunately Ihe skeleton has 

 been dissolved in all Ihe preserved specimens, and I have omitted to 

 make drawings of the living specimens. It was only noticed Ihat the 

 posloral rods are feneslraled. 



In spile of I lie incompleteness of this record of Ihe development of 

 Eucidaris Thmuirsi il is sufficient lo show that if differs most conspicu- 

 ously from Cidurix ridnris (l)orocidtiris papiUalti), Ihe only Cidarid Ihe 

 development of which was studied hilherlo 1 ). The young larva of Ibis 



V) H. Prouho. Hcclicn hcs sur Ic Dororidaris papilhtta ft <|iifl<|iies autri's Echinides >lr 

 la Mi'diU-rranei'. IN.S.S. Arch. /ool. expiT. "oiu-r. 2. SIT. V. PI. XXIII XXV. 



Dr. Kacovitza has kindly sent mi- a pair <>!' spei-imi-nx di'U-rmiiifd ]i\ I'rnulio as l>on, 



