296 



A. KRESS 



a ) différent types of glands were observed, the principal ones being mucus cells 

 (Becherzellen) and a rarer small granular cell. D. pinnatifida has in addition 

 a large granular cell-type. D. coronata and fragilis do not show thèse but 

 have some „ calcium cells " located in the tips of the cerata tubercles. 



b) An attempt has been made to group the free blood cells or amoebocytes 

 into three catégories. 



c) In the tip of the cerata and sometimes in the rhinophores are great numbers 

 of subepithelial „ Wehrzellen ". Thèse glands have a duct through the epi 

 thelium and contain mainly unsaturated fatty acids. 



d) In the connective tissue of the cerata cells of unknown function but rich in 

 nucleic acid were observed = „ cellules spéciales ". 



e ) Typical for ail three species is a granular layer at the base of the cerata which 

 assists in the process of autotomy. 



f) The rhinophore sheath has a thin inner epithelium through which excretory 

 processes take place. This is clearly visible after experiments with trypan blue. 



Problems of autotomy are discussed and the external morphology of the 

 regenerating ceratas described. 



Histology of the regenerating cerata : 



Following a loss of cerata the wound is small. There is no leakage of bod> 

 fluid and in a short time the edges of the epithelium are drawn together through 

 muscular contraction. After that the epithelium in the immédiate area show^ 

 degenerative changes. 



After the second day a small protubérance is visible and first signs of mitosi: 

 can be observed. The cells are very small with large nuclei and distinct nucleoli 

 In the course of growth mitosis increases and the arrangement of cells become 

 more regular. Between the 4th to the 6th day the first mucus-glands appear, anc 

 between the 7th — llth day the granular cells of the epithelium and the ciliatec 

 cells are reformed. In 3 — 4 weeks ail the skin éléments are présent but appea 

 similar to those of cerata in an early stage of development. 



The hepato-pancreatic gland is restored by mitosis in continuity with th 

 remnant of the original gland. The nuclei of the regenerating part show distinc 

 nucleoli. Between the 15th — 20th day the outgrowing tip of the hepatopancrea 

 forms lobes and the cells again look similar to those seen in the very young anima 



After the loss of a body part there is an increasing number of lymphocyte 

 (I) throughout the body. They migrate together with phagocytes to the wounc 

 site the latter removing damaged material. Lymphocytes later differentiate int 

 connective tissue cells, „ Wehrzellen " and „ Cellules spéciales ". The remove 

 tissue is passed mainly into the dorsal vessel and the ventricle. 



