182 EMBRYOLOGY OF THE LOWER VERTEBRATES CH. 



FIG. 102. Larva of Sarcodaces odoe. (After Budgett, 1901. 

 inent-organ. 



of endodermal pockets, they obviously recall gill pouches on the 



MI- hand and cnrl.-ntn -ie pouches on the other. Their position 



suggests a pair of premandibolar Lrill pouches: their function, that 



of forming an excretion (cement), perl laps indicates rather coelomic 



affinities and the present writer suggested (1906) their possible 



correspondence with premandibulai head cavities of other Vertebrates. 



Reighard and Phelps 

 (1908) homologize 



c.o. rr' ' " i~7 - - --- x them with the anterior 



.pair of head -cavities of 

 Elasmobranchs while 

 van Wijhe (1914) sup- 

 ports a homology with 

 the ciliated organ of 

 Amphioxus. 

 Altogether these cement-organs are very interesting and puzzling 



structures and would well repay further investigation. A thorough 



comparative study should be made of their development in the 



archaic Crossopterygians and of their possible, homologues in 



Elasmobranchs. 



Little is known regarding cement-organs in Teleosts, though it 



is probable they will be found to occur in various tropical fresh- 



water fishes. Budgett 



(1901) found a large 



cement - organ on the 



head of the larva of the 



Characinid Sarcodaces 



odoe (Fig. 102, c.o). In a 



larva believed to be that 



of the Mormyrid Hypero- 



pisus bebe he found six 



well-marked cement 



glands on the head which 



in this case secrete fine 



threads by which the 



larva hangs suspended 



in thp water until tin- F "- 103. Teleosti-mi larva.-. Mi| M ...M-.l to W tlnst- of 



HyptropiwbJK, suspended from the rootk-ts in UN 

 V'.lk 18 Used up (1<1-. nes (From Budgett, 1901.) 



103). Il lerotis and 



Gymnarch.il* aN. |><>--rss similar organs very small in tin- latt i 

 tun, 1907). 



Tin; orjjans in tlir-M- \;iri<uis iishrs plTSflit tin- appearance 1 



being ectodermal thiekniin^s: \\- ha\- ae ye1 m> iufonnataon as t< 



whfl h,-r. as may \- siisprdcti, tlicy really originate IVom the 



DICKSTIVK TKACT. Tin- ivs].iral.ry region of the alimentary 

 canal seeded by ihe true li^i-sti\r trae.t and this shows 



"t leSfl pniiuMincmd (lillnviii i;it KMI intn siieeessixe |nniniis 



