78 EMBRYOLOGY OF THE LOWER VERTEBRATES en. 



as they occur in a South American tadpole (Paludicola} 1 but the 

 description fits quite well the mode of development as it occurs in 



Tadpoles generally (Keiffer, 

 Gutzeit),the differences between 

 different species and genera, 

 though of systematic import- 

 ance, being differences in detail 

 such as shape and arrangement 

 of the individual teeth of the 

 comb. 



" Teeth " of Cyclostomes. 

 The horny teeth of cyclosto- 

 rnatous fishes, though they 

 would naturally fall to be 

 treated in the next chapter, 

 situated as they are within 

 the buccal cavity, may con- 

 veniently be considered now 

 owing to their resemblance 

 on a much larger scale and with 

 multicellular structure to the 

 horny denticles of the tadpole. 



The tooth-like spines of the 

 cyclostome are cones of highly 

 cornified epidermal cells. Each 

 tooth develops in the substance 

 of the epidermis (Fig. 46, A) 

 being strikingly like a hair- 

 rudirnent during early stages. 

 Successional spines develop be- 

 neath the bases of the func- 

 tional ones as shown in Fig. 46. 



GLANDULAR DEVELOPMKNTS 

 OF THE EPIDERMIS. In the 

 Anamnia it is usually the case 

 that scattered cells of the epi- 

 dermis take on a glandular 

 function and serve to form 

 a slimy secretion which amongst 

 other functions serves to dimin- 

 ish the " skin-friction " which is 

 tne main resistance to movement 



Fii.. 17. -Illustrating the development of the 

 ri-meut - organ of Lepidosiren as seen in 

 1 ion*. 



A, staK 23; B, HI.-. 



In A tin- r< i< I inn-iil t tin- 1-i-nK'iii i : to IM- a 



tliick-niiix; <>t tli- l'-.-|. lay-,- .,1 tl <-to.i.-i in ; in 1} 



anil (' tin- sii|x-i-licial layi-r lia-. ilisa|i|M-an-il MM-I- tin- 

 Uiicki-iH-'l -lamlnlai an-a ; in l> t In- m.-an i> i-oninn-n- 



ar cullci-ti-d 



: ;,::;;; ';;;;."" " '" through water. Such ,.nioell..I.-..- 



glands ina.y l>ecome collected 



together In I'nrin mull ic-lliilar glands. ( M lln-sr Ilic most rnnspirimus 

 examj'l"-- BM found, OUteide 'the Maniinalia, in tin- Lim^-lisli<>s and 

 Aiujiliibians \\ ln-iv Mn-y I'MI -in 1 In- llask-'4lands and the cniuMit -<T 

 I'roh.-ihly P,fu$OOnMCulnf(t iicconliii^ to Boulen^r 



