1048 



SUBMAMMALIAN VERTEBRATES 



do transport their eggs and larvae by one 

 means or another. In most cases, this is a 

 matter not only of specialized behavior but 

 of some morphologic modification. Aiytes 

 obstetricans, a European form, is popularly 

 called the midwife toad. Actually, it is the 

 male of this species which manages to wind 

 about his hind legs the strings of eggs which 

 the female has laid. Here they stay, encased 

 in their sticky jelly, until they hatch. The 

 female Hyla goeldii, a South American frog, 

 carries a mass of incubating eggs on her 

 back with the aid of a low skin fold which 

 helps to form a kind of shallow receptacle 

 (Boulenger, 1895 ) . At least four other genera 

 of South American tree frogs similarly trans- 

 port incubating eggs as a mass, partly or 

 completely covered by a flap of dorsal skin, 

 or individually, each egg in a separate 

 pocket of skin on the back (Noble, 1931). 

 Bartlett (1896) reported to the Zoological 

 Society of London how the eggs are placed 

 on the back of the Surinam toad, Pipa ameri- 

 cana. He and a keeper observed the process 

 in the reptile house at the Zoological Gar- 

 dens. Late in April two pairs of the frogs 

 were seen in amplexus. The male had firmly 

 grasped the lower abdomen of the female, 

 his body extending caudal to hers. Her "ovi- 

 duct" was protruded more than an incli, 

 arching between the belly of the male and 

 the back of the female. (Subsequent dissec- 

 tion by Boulenger of a female which died 

 during oviposition showed that the "oviduct" 

 was actually an "ovipositor, formed by the 

 cloaca.") The male squeezed the sac-like 

 ovipositor and moved it about, thus direct- 

 ing the even placement of the eggs. The lat- 

 ter stuck to the back, and the ovipositor 

 later was retracted. It is known (Parker and 

 Haswell, 1921) that the eggs eventually sink 

 into cavities which develop in the spongy 

 dorsal skin, that lid-like structures form 

 over the cavities, and that the larvae remain 

 in these convenient, individual containers 

 until they metamorphose. What regulates 

 the modification of the dorsal skin so that, 

 at the proper time, each egg can "implant" 

 in this strange site? 



Tadpoles of the genera Dendrobates and 

 Phi/llobates attach themselves by buccal 

 suckers to the back of an adult male (Bou- 

 lenger, 1895). The larvae of Arthroleptis 



seychellensis, a frog found in the Seychelles 

 Islands of the Indian Ocean, swim to the 

 back of the adult. Here they attach them- 

 selves, not by buccal suckers but by a sticky 

 ectodermal secretion. Contact is always be- 

 tween the ventral skin of the larva and the 

 dorsal skin of the adult (Brauer, 1898). 



Reptiles 



There appear to be no reports of morpho- 

 logic specialization for the external trans- 

 port of reptilian eggs or young. 



XI. Ovary; Ovogenesis; Ovulation 



Fish 



The ovaries of fish range from primitive 

 structures to rather complex organs which 

 may combine functions of the mammalian 

 ovary, oviducts, uterus, and even, to an ex- 

 tent, the mammary gland. On the other 

 hand, detailed knowledge regarding the geni- 

 tal systems of most species of fish is sur- 

 IH'isingly scanty, particularly in terms of 

 histologic detail. Surely this is an impor- 

 tant and fascinating area for research. 



The brook lamprey, Entosphenns wilderi, 

 which has been carefully studied by Okkel- 

 l)(>rg (1921), attains its full body length 

 while still a lar\-a. Then it metamorphoses. 

 Now, in xAugust or September, comes the 

 climactic stage of its life. The gonads ma- 

 ture, growing swiftly to the point where they 

 occupy all the body cavity. The digestive 

 tract atrophies. Thereafter the lamprey eats 

 nothing. It l)reeds the following April, and 

 then dies. There is a single testis or ovary 

 in the sexually mature animal. The eggs are 

 enclosed in follicles; the latter are believed 

 by Okkelberg to be homologous with the 

 cysts of the testis. The mature ova are, as 

 in cyclostomes generally (Hoar, 1957a), 

 shed into the coelomic cavity and then 

 escape to the exterior by way of abdominal 

 pores, urogenital sinus, and urogenital pa- 

 pilla. 



In the basking shark, an elasmobrancli, 

 only the right ovary develops (Harrison 

 Matthews, 1950). It may contain about 

 6,000,000 ova, 0.5 mm. or more in diameter 

 and possessing some yolk. When the ripe 

 follicles rupture, the ova escape into a pouch 

 inside the ovary, then are propelled into the 



