EMBRYOLOGY AND LARVAL DEVELOPMENT OF TELEOSTEAN FISHES. II9 



In young fish 5.2 mm. in length (fig. 75) the dorsal and anal fins are becoming 

 differentiated. In the posterior abdominal region the intestine is convoluted, as is 

 characteristic of the young of many clupeoid fishes. The body remains almost color- 

 less. The chromatophores along the intestine and at the base of the ventral-fin fold 

 are less conspicuous than in the earlier stages. 



BREVOORTIA TYRANNUS (Latrobe). MENHADEN, POGY. 



Spawning. — For years data on the spawning habits of the menhaden have been 

 sought with little success. Observations on the movements of the schools and exami- 

 nations of the reproductive organs lead to the belief that in New England spawning 

 takes place in late spring or early summer and that from Chesapeake Bay southward 

 the season is late fall or early winter. Some reasons have been advanced for belie\'ing 

 that in the Chesapeake region, at least, there are two spawning seasons. A very 

 important addition to our knowledge of the life history of this species has recently 

 been made by W. W. Welsh, of the Bureau of Fisheries, in identifying the larvae. His 

 specimens were about 24 mm. long, taken in St. George Sound, Carabelle, Fla., Janu- 

 ary 15, 1913. On February 22, 1914, examples about 30 mm. in length were taken 

 near the mouth of the Potomac River, off Piney Point, Md., by the junior author, 

 and on October 21, 1914, specimens about 20 mm. in length were collected in Woods 

 Hole Harbor. 



Observations made at Woods Hole this season indicate that the main body of 

 fish spawn in June and that spawning continues throughout July and August and 

 apparently later, as the Grampus obtained eggs and larvae to the westward of Marthas 

 Vineyard and in Nantucket Sound the last week in October, 191 5. About June 30 

 larvae were common in the plankton in the harbor and were not rare as late as July 

 20. The young, with most or all of the adult characters, were not infrequently taken 

 in abundance between July 10 and August 10. For several days about July 21 adult 

 fish were present in Vineyard Sound. Examinations of the reproductive organs of 

 some of these fish indicated that they were about ready to spawn, and others were 

 spent. Some of the males had enlarged testes with active spermatozoa, and the 

 ovaries of some of the females were greatly distended. 



Individual eggs were occasionally tajcen in the tow in the harbor throughout July. 

 On August 20 they were quite abundant in the plankton off Gay Head and were still 

 present on the 24th. 



Eggs. — The eggs are highly transparent, spherical in form, and 1.4 to 1.6 mm. in 

 diameter. The perivitelline space is very large. In this respect these eggs resemble 

 the eggs of the shad and the European pilchard. The yolk sphere is approximately 

 0.9 mm. in diameter and contains a transparent oil globule 0.12 to 0.14 mm. in diameter. 

 The egg membrane is thin and horny. 



Embryology. — The embryological development of these eggs does not differ essen- 

 tially from the course of development as outlined above for the eggs of Tautoga onitis. 

 An advanced stage of cleavage is illustrated in figure 76. Figure 77 illustrates an 

 advanced stage in the differentiation of the embryonic axis. Figure 78 illustrates an 

 egg shortly after the closure of the blastopore. Itie embryo is relatively long and 

 slender and at this time extends more than two-thirds around the circumference of the 

 yolk sphere. 



