io TIL MORTENSEN, (Schwed. Siidpolar-Exp. 



Also the pedicellariae afford some differences. In the specimen from St. 17 they 

 are invested by an unusually thick skin, but otherwise the structure of the valves 

 is the same as in the normal specimens; in the specimen from St. 22, on the other 

 hand, the valves differ rather considerably from those of the normal specimens, 

 the opening being broadly triangular with the lower edge almost or wholly straight 

 (PI. XIII Fig. 9). 



On a closer examination I find that these spe- 

 cimens show in their radioles a structure quite similar 

 to that which I have described for Rliynchocidaris 

 £/°oo° ° 5 ^<c?c> triplopora (Op. cit.). The curious tubes protruding 



0~O o o 00 <=> ° 0 O ° O ^ 



^0 o ° o ^°°°°°°^q o % q through the thorns of the radioles are also found 



a °^°°o€°°°J*?,§^£ here, though not so strongly developed as in that 



°o°o° o°°°^>* species. In one case I have further found in a 



°° 0 o° 0 ° section of a radiole an organism* boring in the chalk 



matter, quite similar to that which I have described 



Fig. 3. Transverse section of radiole from frQm th&t species _ j n shorti T think ifc can scarce ly 

 a specimen of Ctenocidaris speciosa in- 

 fested with Echinophycis. 5 °'i. ^ e doubted that these specimens are infested with 

 EcJiinopJiyces, though I have, unfortunately, not 

 found anything corresponding to the ''spores" found in RJiyncJiocidaris. 



The differences from the normal specimens occurring in these two specimens 

 I must then suppose to be due to the reaction against the parasite. It is further 

 worth noticing that genital pores have apparently not yet been developed in these 

 specimens, though they have appeared in the normal specimen of 18.5 mm. But on 

 the other hand these specimens show the curious feature of having a small opening 

 in the median interambulacral line at the ambitus (PI. XIII Fig. 1). In view of the 

 fact that in RJiyncJiocidaris the genital openings have become transferred to the edge 

 of the peristome in specimens infested with EcliinopJiyces, it seemed not unreasonable 

 to suggest that these curious openings in the middle of the interambulacra are the 

 abnormally placed genital openings. In order to state this definitely I have opened 

 one of the two specimens and found that this small interambulacral opening is really 

 the genital opening. As was the case in RJiyncJiocidaris, the normal, genital duct 

 exists but is, evidently, out of function. From the genital gland a new efferent 



* In the same radiole I find here and there in the meshes made by the »hairs» on the ostracum a 

 worm-like organism, irregularly rolled up — the same I found in the radioles of Rliynchocidaris. It looks 

 very much like a Nematod. As I did not feel myself able to put beyond doubt whether it really is a 

 Nematod or something else, I sent a preparation of it to my friend, the eminent specialist in Nematods, 

 Dr. L. JagerskjOld in Gothenburg, asking him to examine it. He kindly informed me that he thought it 

 most likely a Nematod-Larva: but the material did not allow him to state anything more definitely about 

 the animal.' — There can thus scarcely be any doubt that the worm has nothing to do with the abnormal 

 changes in these specimens; it only takes a place on the infested spines. 



