SKELETON AND LARYNX OF XENOPTTS AND PIPA. 115 



Thierreicli von einer Cartilago thyreoidea im Sinne des Sauge- 

 thierschildknorpels sprechen." But, as already objected by 

 "Wilder (42. p. 291), if we apply tbe term " thyroid " to products 

 of the fourth and fifth visceral arches (i. e. the second and third 

 branchial arches), we must certainly not employ the same word 

 for structures developed beMiid the fourth branchial arch, 

 although perhaps the two may be physiologically identical. 

 Mayer (25. p. 541) had previously applied tbe term " os thyreoi- 

 deum " to the anterior part of the floor of tbe larynx of Pipa (not 

 the whole of it, as Grronberg appears to intimate) , but he prob- 

 ably did not intend the comparison to be taken too strictly. It 

 is sufficiently misleading to employ the same word thyrohyal ia 

 Anura and Mammalia for structures only functionally similar; 

 but custom has so familiarized us with the enormity that we have 

 come to associate difi'erent morphological ideas with the word 

 according to the animals to which it is applied. Still, this fact 

 does not warrant the introduction iuto aa already too involved 

 literature of fresh sources of confusion. 



It were rash to institute, as many do, a system of classification 

 based on the characters of a single organ, or even a few associated 

 organs ; but since the systematist has recourse to as many 

 structural differences and resemblances as are within his know- 

 ledge when drawing up a scheme of classification, it may be well 

 to ascertain what weight may be allowed to the various details 

 set forth in the preceding pages when applied to the solution of 

 the problem of natural affinity. Both Xenopus and Pipa have 

 elongated bronchi, which are absent in all Phaneroglossa ; but it 

 is somewhat doubtful whether the bronchial cartilages supporting 

 them have not originated independently in the two genera (see 

 p. 71). The curious lobe of the lung arising from the dorsal 

 surface of the anterior end of the bronchus in the larval Xenopus 

 is not represented in Pipa ; on the other hand, the outgrowth 

 or lobe on the mesial surface of the lung of Pipa finds no 

 counterpart in Xenopus. With regard to the larynx, a greater 

 difference exists between this organ in the male and female of 

 Pipa than in the females of Pipa and Xenopus. In the male of 

 both genera the laryngeal complex is connected by ligament with 

 the bulk of the hyobranchial skeleton ; but, since these ligaments 

 do not correspond morphologically, it is evident that we are 

 dealing here with nothing more than an adaptation to subserve 



