1 82 CARL L. HUBBS. 



enemies away from the eggs or young; the gestation of the young 

 within the mouth or blood pouch ; the enclosure of the eggs in 

 a tough capsule, or finally by the actual development of the 

 young within the oviduct or ovary of the mother. 



The degree to which this viviparity has become perfected varies 

 widely in the different groups of viviparous fishes. Some 

 teleosts, such as the scorpaenoid fishes, give birth to thousands 

 of minute embryos, still nourished by a relatively large yolk-sac ; 

 while others bear only a few young, but fully developed and 

 capable of self-support, almost immediately after birth, in the 

 normal manner of adult fishes. In some of these, as the 

 Pceciliidae, the embryos are nourished by the yolk in the egg, and 

 a meroblastic type of cleavage persists. In the Embiotocidae or 

 viviparous perches on the other hand, the yolk is greatly reduced 

 in bulk, the cleavage approaches the holoblastic type (according 

 to Eigenmann, 1894, etc.), and the embryos are profoundly modi- 

 fied structurally. 



The viviparous perches (see Figs. I and 2) comprise a com- 

 pact group, the family Embiotocidse (and the suborder Hol- 

 conoti) of the Acanthopterygii or spiny-rayed fishes. The group 

 is relatively old, apparently, for the many structural features cor- 

 related with viviparity are common to all of the species, and hence 

 became fixed before the extensive generic differentiation char- 

 acteristic of the family arose. Almost all of the species are 

 generically distinct from the others, another situation suggesting 

 the age of the group (cf. Eigenmann and Ulrey, 1894; Jordan 

 and Evermann, 1898, and Hubbs, 1918). The immediate rela- 

 tionships of the Embiotocidse not being apparent, nothing definite 

 can be said concerning the origin of their viviparity. 



The viviparity of the embiotocids was first definitely made 

 known by Dr. A. C. Jackson in 1853, in a letter to the elder 

 Agassiz. These fishes then almost immediately attracted the at- 

 tention and study of a number of zoologists, among whom may 

 be mentioned both Louis and Alexander Agassiz, Gibbons, and 

 Girard. Later Ryder, and particularly Eigenmann, studied their 

 embryology, and Jordan and Gilbert, Eigenmann and Ulrey and 

 others also studied the group (see bibliography). I have re- 



