100 PROCEEDINGS OF THE ACADEMY OF [Feb., 



mal glands of D. gyrociliatus, and found that glands similar to the 

 Klebsdriisen occur not only on the caudal appendage, but on the 

 head and on the anterior part of the trunk as well, where they form 

 ringlike groups corresponding to certain shining belts. Moreover, 

 each of these glandular rings was placed before a corresponding ring 

 of cilia. In the White Sea Dinophilus Schimkewitsch (1895) found a 

 similar condition. These metamerically arranged glands Repiachoff 

 considered to be true mucous glands, while the Klebsdriisen were of a 

 different nature. The results of these authors are difficult to reconcile 

 with one another, in the light of my own observations, since, as has been 

 shown, the true mucous glands are comparatively inactive, and would 

 therefore be unlikely to function as adhesive glands. On the other 

 hand, the non-mucous glands — those of the third type — are function- 

 ally very active and constantly emitting their secretion, and these 

 might very well correspond to the Spinndriisen, and possibly also to the 

 Klebsdriisen of Korschelt. A final decision, if it is possible to arrive 

 at one, must however rest on direct observation of the living animal, 

 and therefore be for the present postponed. 



Muscles. — The body wall is provided with only two sets of muscles ; 

 one of these is composed of longitudinal muscle fibres which extend 

 throughout the whole length of the trunk, the other comprises a few 

 muscles traversing the head. A careful search with a one-twelfth oil 

 immersion lens failed to yield any convincing evidence of the presence 

 of a layer of circular or oblique muscles, although in one or two cases 

 isolated circular muscles were found. One of these is shown in fig. 8, 

 on the right side of the figure. The negative evidence in the case 

 seems fairly conclusive, inasmuch as the longitudinal muscles, as well 

 as other muscle fibres, stain intensely in the stain employed, iron 

 hsematoxylin. Other muscle fibres should therefore, if present, be 

 also plainly discernible. In this connection it is to be noted that 

 Protodrilus Hatschek (ISSO) also lacks the layer of circular muscles. 



The longitudinal muscles are distributed in three pairs: (1) a 

 medio-ventral pair lying in the mid-ventral line (fig. 6, v.l.m. 1); (2) a 

 ventro-lateral pair (v.l.m. 2), the two members of which lie at an angle 

 of about 45° from one another, as seen in transverse sections of the 

 trunk, and (3), corresponding with the latter, in the dorsal half of the 

 body, a dorso-lateral pair (d.Lm.). Each muscle is composed of a 

 mnnber of long spindle-shaped fibres, arranged in a single layer in close 

 contact with the hypodermis. Of these fibres the medio-ventral pair 

 of muscles has the fewest, not more than two or three being seen on 

 each side, in transverse sections; while the ventro-lateral and dorso- 



