23 



lion \v;is undertaken repeatedly, none of the cultures proved very suc- 

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

 ([ualily. The youngest stages were excellent, but as soon as the formation 

 of Ihe IMuleus was about to begin, the larva' became abnormal and died. 



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

 size — and very transpaicul. The developing embryos are most beautiful 

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

 (Mslincl. () hours after fertilization they were swimming blastula*; about 

 20 hours after fertilization the gastrula stage was reached. 



The young larva is a very curious object, rather unlike other young 

 l-.chinoderm larvtt. 11 lias the shape of a biconvex lens, with a perfectly 

 circular haiu!, and recalls, in fad, a Trochophora by its shape (PI. V 

 i'ig. 1). while 11 is, of course, cpiite dilTerenl from a Trochophora in its 

 anatomical structure. The digeslive organs are very small, the moulh 

 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. It was 

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

 in one case 1 succeeded in getting them a Utile farther in their develop- 

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

 ance, normal. It is no less peculiar than Ihe younger stage. The postoral 

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

 specimen available — Ihe left arm is slightly upwards directed. It 

 has been corrccled in liie figure to suit Ihe rigiil arm, whicli is (|uile 

 horizontal and has all the appearance of having preserved ils natural 

 form and direction, while the other has more the a])])earaiice of being 

 slightly dislorled. However, since the skeleton is dissolved, il is impos- 

 sible to ascertain deliniU'ly wiiich is the correct form of Ihe arms — and 

 I have omilU'd lo notice anything about il Irom Ihc living specimens.) 

 Ollu'i- |)i()cesses arc nol yel indicaled; Ihci-c is only an elevalion indicating 

 the oral and anal lobe. This larva is (i days old. The skclclon was begin- 

 ning lo form al Ihe age of three days. I'nI'orlunalely Ihe skeleton has 

 been dissolved in all Ihe jireserved specimens, and 1 have omilled lo 

 make drawings of Ihc living specimens. Il was only noticed Ihat the 

 postoral lods arc fenesli-ated. 



In spile of Ihc incom])leleness of Ihis record of Ihc (levelo|mienl of 



I'Aici({(tris ThoiKirsi il is sufficienl lo siiow Ihal il dillers most consjiicu- 



onsly from (jditris ridaiis (Doiocidaris iHipiUala). the only Cidarid the 



develo])menl of which was studied hitheilo'). The young larva of this 



') II. I'rouho. Hocheniu's siir lo Doroiidaris papillala ct (|ui'l(iues autres fidiinitlos de 

 la Mediterranec. 1S.S.S. .\itIi. Zool. cxper. gd-ndr. 2. Si^r. V. PI. XXIII— XXV. 



Dr. i^acovitza lias kiiully soiil iiio a pair of specimens determiiieil l)y Prouho as Ihiru- 



