ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 733 



Vermes. 

 a. Annelida. 



Criodrilus lacuum.* — Dr. A. Collin has made a detailed investigation 

 of this Oligocheete. Exceptionally large specimens from the Spree were 

 as much as 30 centimetres long, and had 450 segments. The clitellum, 

 which has been overlooked by all writers except Dr. Benham, is not 

 distinctly marked off, but is merely a slight swelling ; its colour, like- 

 wise, differs but little from that of the rest of the body, and it is only by 

 its histological structure that it can be recognized. 



This worm has, in Berlin, as yet only been found in the Tegeler-See 

 and in the Spree, where it lives on mud rich in organic substances. The 

 author was able to keep specimens alive for some months in a glass 

 basin, but they never became sexually mature ; as they live, naturally, 

 at a depth of from 8 to 10 feet, the difference in the pressure may be the 

 cause of this. In Berlin the worm is sexually mature in June and July. 

 The cocoons are chitinous, and about 5 centimetres long ; they exhibit a 

 slight indication of a transverse marking, which is probably the expression 

 of the several segments of which the cocoon is formed. 



The cuticle is like that of Lumhrieus, but much thinner ; there is no 

 longitudinal or circular arrangement of the fibres, but an oblique one 

 only ; the mechanical disadvantage of circular fibres to the contraction 

 of the longitudinal muscles is obvious. The whole of the hypodermis, 

 especially in the hinder region, is traversed by closely set, fine, 

 capillary vessels which aid in respiration. Between the cylindrical 

 there are here and there filamentar cells, with a swelling in the middle, 

 which corresponds to the position of the nucleus. Unicellular glands 

 are not nearly so numerous as in Lumhrieus. The hypodermis of the 

 cephalic lobes differs somewhat from that of the rest of the body ; it 

 consists of extremely delicate cylindrical cells, which are twice as long 

 as those of the hypodermis of other parts of the body. 



A number of the cells of the hypodermis of the cephalic lobes and 

 of the first segment are specially differentiated, and form groups of 

 goblet-shaped cells, which appear to have a gustatory function. The 

 circular muscles consist of flattened fibres which, in transverse section, 

 do not exhibit any lumen ; with high magnifying powers, however, a 

 darkish line may be seen in the middle, and this indicates the lumen of 

 the compressed tubular fibre. There are scattered nuclei, which belong 

 to the intermuscular connective substance between the muscles. The 

 arrangement of the longitudinal muscles of Criodrilus differs somewhat 

 from that of the Lumbricidte. Eosa has distinguished a ventral, four 

 lateral, and two dorsal muscular bands. Dr. Collin, however, does not 

 find any break in the median dorsal line, but only a thinning of the 

 layer. Into the septa which separate the bundles of muscular fibres 

 there are inserted transverse muscles, which extend to the enteric tract, 

 and the chief longitudinal vessels. The bundles of the Lumbricid^ 

 consist of two regularly arranged rows of muscular lamellae, which are 

 grouped around the central lamella, but in Criodrilus they consist of a 

 number of muscular lamellae which are irregularly scattered in the space 

 between two neighbouring central lamellaB. The separate muscular 

 fibres can be easily isolated by potash. 



* Zeitschr. f. Wiss. ZooL, xlvi. (1888; pp. 471-96 (1 pi.). 



