REPORT ON THE MYZOSTOMIDA. 15 



THE CYSTS OF ANTEDON ROSACEA (PI. IV.). 



In 1885 P. H. Carpenter^ directed attention to peculiar sweUiugs which he very 

 frequently obsei-ved on the pinnules, and less frequently on the arms, of the Antedon 

 rosacea of European seas. From the results of the study of deformities produced by 

 Myzostomida on Crinoids, Carpenter could not but regard it as probable that 'the 

 malformation was in this case also referable to the same cause. 



From the aljundant material entrusted to me, I have in figs. 1 to 3 represented some 

 of these deformities, magnified five times. The pinnule malformations are extra- 

 ordinarily numerous, and occur on Aiitedgn rosacea from the most diverse localities, as 

 Carpenter has noted. Sometimes they are hardly noticeable thickenings of a single joint, 

 or of two, less frequently of three adjacent joints (figs. 3, a and 2, h), sometimes larger 

 spherical dilatations towards the adambulacral side (fig. 1, a). Somewhat rarely dilata- 

 tions occur like that represented in fig 2, a, which is really only a pit surrounded by a 

 thickened wall. On the other hand there are not unfrequently two or three such swellings 

 on one and the same pinnule, and on a single arm of an Antedon rosacea from Milford I 

 counted seven of the malformations, and in all fourteen characteristic swellings on one 

 individual. 



Less numerous are the arm-swellings, such as that represented in fig 2, c. On that 

 specimen (collected by the " Vettor Pisani " near Gibraltar), three distinct deformities 

 occur in close approximation. The very slight arm-swelling extends over two joints, and 

 is tolerably uniform on either side. I have observed, however, one-sided conical swellings 

 of the arm-joints, sometimes combined with an enlargement of the basal joint of the 

 attached pinnules. 



I have opened fourteen of these malformations of Antedon rosacea under a lens, 

 and, after decalcifying them, have cut longitudinal sections, but in no case have I found 

 a Myzostoma or any other encysted organism. On the contrary, both in the various 

 pinnule deformities and in the arm-swellings, I found a roundish brown foreign body, 

 which was apparently the cause of the deformity, though it was not possible for me to 

 determine anything definitely as to itg nature or origin. 



In fig. 4 one of these bodies is represented, which I removed from the pinnule 

 swelling of an Antedon from Cumbrae. The diameter of the sphere measured 0-3 mm., 

 and the substance was distinctly divisible into a strongly refracting cortical layer and 

 an opaque granular internal mass. The former was radially divided into cell -like 

 portions, and had quite the appearance of cylinder epithelium both in optical section 

 (a) and on surface view (c). There was not however any sharp boundary between the 

 outer layer and the central mass. The whole had thus the appearance of a superficially 



segmented ovum. 



' Nature, 1885, vol. xxxii. p. 391 ; voL xxxiii. p. 8. 



