1 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. V. 



Woolman and Pcecilia occidentalis (Baird & Girard), have the anal fin 

 of the male placed well forward and modified into an intromittent 

 organ sueh as is characteristic of Heterandria, Pcecilia and the like. 

 In the other species the anal fin of the male has its normal position 

 and size, but it is slightly modified by the shortening of the first five 

 or six rays, and their slight separation from the rest of the fin by a 

 shallow notch. This modification was first noticed by Gunther in 

 Characodon later alis Gunther. It was also described by Bean in 

 Zoogoneticus robustus (Bean), and by Jordan and Snyder in Goodea 

 atripinnis Jordan, but no significance was attached to it. Just 

 what part this fin plays in fertilizing the eggs in the body of the 

 female is not known, but it evidently plays a prominent part in this 

 operation. 



I was so fortunate as to collect these fishes during the breeding 

 season and thus their viviparity was easily proved. The largest 

 killifish known from the Lerma basin reaches a length of 8 or 10 inches. 

 The accompanying figure was made from a photograph of the largest 

 female of this species I was able to obtain. The ovary consists of a 

 membranous sack with a number of infolded partitions. Removing 

 a portion of one side shows the ovary full of quite well developed 

 young. The little fishes are not arranged in any definite order. 



The spawning time of these fishes is near the close of the dry season. 

 At this time the water is more concentrated, as is also the food on 

 which the young must feed. The aquatic insects, crustaceans and 

 small fishes which would feast on the eggs if deposited then are also 

 more concentrated, so that depositing the eggs at this time would 

 mean considerable destruction to the species. As it is, the young 

 are born in a well-developed stage, and reach some size before the wet 

 season sets in. They are then perhaps in the best condition to become 

 widely distributed as the volume and area of water increases. As 

 the dry season approaches again, and the small streams and ponds 

 become dry, some of these small fishes perish. They are, however, 

 present everywhere to establish themselves in any body of water 

 which may carry them through the next rainy season. 



The gestation of many tropical fishes presents some strange pecu- 

 liarities. Some of the catfishes carry the eggs in the mouth till hatched, 

 while a few others are thought to be viviparous. Viviparity among 

 the tropical killifishes seems to be the rule rather than the exception. 

 It would seem that in the tropical fresh waters of America there is 

 much more provision made for the care of the young than in the cooler 

 waters of the northern continent. 



It is rather surprising to find such a large number of Chirostoma 



