STRUCTUEE, ETC., OF CEEATA OF NUDIBEANCHS. 43 



of serial sections, giving the exact histological relations of the 

 dififerent parts of the body, has apparently not up to now been 

 made use of by any of these writers on the structure of the 

 Nudibranchiata. 



My specimens have been collected in the Liverpool Bay 

 district, either in the neighbourhood of the Biological Station 

 on Puffin Island, or at Hilbre Island, in the estuary of the Dee. 

 They were generally killed with Kleinenberg^s picric acid, 

 hardened with graduated alcohols, stained in picro-carmine, 

 embedded in paraffin, cut with the Cambridge ''rocking" 

 microtome, and mounted in Canada balsam. Some were 

 soaked in gum, cut in the freezing microtome, and examined 

 in water, in glycerine, and in Tarrant's solution for comparison 

 with the others. My laboratory assistant, Mr. J. A. Clubb 

 who is working along with me in the collection and identifi- 

 cation of the Nudibranchs of the district for the Reports upon 

 the Fauna of Liverpool Bay, has given me a great deal of 

 assistance in preparing the specimens and cutting the sections. 



Doris. 

 In Doris (PI. VI, fig. 1) there is a pair of short stout 

 laminated rhinophores on the head, and a clump of well- 

 developed branchiae near the posterior end of the dorsal 

 surface of the body. There are no cerata or other dorsal 

 processes. The branchiae are in the form of a number (usually 

 6 to 12) of pinnate plumes arranged in a circle round the 

 anus. In sections the branchiae have the structure shown in 

 fig. 2. The branches are subdivided and the surface is very 

 irregular. The epithelium varies from nearly squamous to 

 columnar, and there are large blood-lacunse forming irregular 

 spaces and passages and coming into close relation with the 

 surface, being only separated from the ectoderm in some 

 places by a very thin layer of structureless connective tissue. 



Ancula. 

 In Ancula cristata (fig. 3) there are rhinophores, well- 

 developed branchiae, and large but simple unbranched cerata. 



