VII] 



ANATOMY 



121 



This loop is called the trochus; it 



usually consists of more powerful cilia 



than the rest of the velum, which is 



termed the cingulum. The groove 



between the two bands in which the 



mouth lies is covered with fine cilia. 



In the genus Rotifer the trochus is 



composed of two almost circular lobes, 



which were described as wheels by the 



first naturalist who observed them, and 



this circumstance, as we have said, 



suggested the name given to the genus 

 and afterwards bestowed on the whole 

 phylum. 



Within the cuticle which covers the 

 body is the ectoderm. This takes the 

 form of a protoplasmic layer with 

 scattered nuclei, showing no cell-out- 

 lines. It surrounds a spacious primary 

 body-cavity, which contains a fluid with 

 no amoebocytes ; in this float the various 

 organs of the body connected more 

 or less closely together by connective 

 tissue-cells. Connective tissue is 

 the name given to a tissue like the 

 parenchyma of Platyhelminthes and 

 Nemer tinea, consisting of stellate cells 

 united to one another by their pro- 

 cesses, but in which, along the outer 

 margins of these united cells, tough 

 fibres are secreted which cross one 

 another and give firmness and tensile 

 power to the whole. Fibres are 



very scantily developed in the I- Circle of tentacles bearing bristles, 

 connective tissue of Rotifera. 

 The cuticle of the ectoderm is 

 the most important part of the 

 skeleton. The muscles do not 

 form a continuous layer under- 

 neath the ectoderm as is the 

 case with the Platyhelminthes 

 and the Nemertinea but consist 



FIG. 51. 



Diagram of Floscu- 

 laria. 



2. Velum. 3. Mouth leading to vesti- 

 bule. 4. Brain. 5. Oesophagus 

 hanging like a funnel into the crop. 

 6. Mastax with trophi. 7. Stomach. 

 8. Eectum. 9. Opening of cloaca. 

 10. Strands of muscles. 11. Yolk- 

 gland part of ovary. 12. Ovarian 

 part of ovary. 13. Oviduct. 14. Ex- 

 cretory duct opening into 15, urinary 

 bladder. 16. A tag with a tuft of 

 cilia. 17. Longitudinal and circular 

 muscles in foot. 



