ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 69 



radial arrangement was an adaptation to the meclianism of fixation, 

 or of the peculiar type of fixation, the want of it, as in Stelechopus^ 

 which doubtless is a freely moving form, must be regarded as the 

 primitive arrangement, and thus intensifies the affinity to the 

 Tardigrades. It is interesting to find several forms entirely unpro- 

 vided with suckers, though in some they may exist as mere rudi- 

 mentary bodies ; in one species (M. cahjcotyle) the suckers are stalked. 

 The suggestion so aptly made by von Willemoes-Suhm that some of 

 the Myzostomida were in all probability dioecious, has been amply 

 verified by von Graff's researches. The two sexes when inhabiting 

 the same cyst are at times unlike in appearance, the female being 

 usually fifty to a hundred times as large as the male. 



Of the sixty-seven species of Myzostomes described, elaborate illus- 

 trations are to be found of all the new ones, while one plate is altogether 

 devoted to the illustrations of Stelechopus liyocrini. The body in this 

 new type has a general similarity to a Tardigrade. Unfortunately 

 the few specimens found being mounted in Canada balsam were 

 somewhat altered in contour, but enough remained to surely indicate 

 that the lateral margins of the body are nearly parallel in the middle, 

 and become somewhat narrowed at either end. There is a conical 

 caudal appendage. The largest specimen measured 3-5 mm. long, 

 with a greatest diameter of • 9 mm. ; the cuticle was chitinous ; the 

 parapodia, five on each side, were independent in action one of the 

 other. The specimens were taken from species of Hyocrinus and 

 Bathycrinus, off the Crozets, at depths of 1000 and 1375 fathoms. 



Anatomy of Balanoglossus.* — An addition to our knowledge of 

 this interesting form has been made by J. W. Spengel. 



The so-called proboscis is the chief organ of movement ; it is made 

 up of an outer epidermic and two muscular coats ; the innermost 

 of these, the longitudinal coat, is extremely thick, and only leaves a 

 very small cavity in the interior of the proboscis, which is partially 

 filled by a network of connective-tissue cells ; this cavity communicates 

 with the exterior by one {B. minutus, &c.) or two {B. hupfferi) pores ; 

 the external half of the canal thus formed is ciliated ; the pores as 

 well as the muscular walls are the remains of the " water-vascular 

 sac " of the Tornaria. The base of the proboscis is supported by a 

 skeletal structure having much the shape of an hour-glass, two pro- 

 longations from which surround the alimentary canal ; this structure 

 is formed by the epithelium of the alimentary canal, and is a special 

 local thickening of its basement membrane. On the dorsal side in the 

 same region of the body is a sac-like structure which corresponds 

 to the " heart " of the Tornaria ; it does not appear, however, to have 

 been well named, as no communication with the vascular system was 

 observable. The next section of the body, the " collar," contains the 

 anterior portion of the gut ; the body-cavity is formed by irregular 

 spaces left between the strands of connective tissue, which com- 

 municate with the exterior by f wo pores. On the dorsal side is a 

 longitudinal blood-vessel which anteriorly fills up the space between a 



* MT. Zool. Stat. Neapel, v. (1884) pp. 494-508 (1 pi.). 



