260 . DEVELOPMENT OF A NON-AQUATIC TADPOLE. 



have a more pointed snout and are differently coloured. The 

 interesting point to note is the apparent pre-determination of 

 sex in the egg. 



According to Dr. Emil Witschi* differences may be detected 

 very early indeed in the development of the testis and ovary. 

 Notwithstanding these facts, there would appear to be no doubt 

 that semi-starved tadpoles tend to become males, and very 

 possibly in the case of Anhydrophryne if a newly transformed 

 frog from a^ large egg received only a minimum amount of food 

 it would become a male, the female tendency being overcome by 

 the reduced metabolism of semi-starvation. It would be interest- 

 ing to know whether the smaller members of the egg-clutches 

 of egg-laying animals tend to become males when other factors 

 are equal. In this connection it may be remarked that in the 

 case of Hydroids which can-y both male and female gonangia 

 or sporosacs on the same colony, the male gonangia always tend 

 to occur in those ])laces of the colony where there w'ould be a 

 less abundant supply of nutritive substances. 



Summary. 



1. Segmentation meroblastic, blastoderm syncytial, nuclei 

 creep down into superficial protoplasmic layer surrounding the 

 yolk-mass to form enveloping ectoderm. Inner portion of thick 

 syncytial blastoderm becomes mesoderm, nuclei from enveloping 

 layer invade the yolk-mass, and at a comparatively late period 

 when neural tube, notochord and archenteron are established the 

 whole yolk-mass breaks up for a brief period into moderate-sized 

 cells. The cause of this peculiar mode of early development must 

 undoubtedly be referred to the presence of the excessive quantity 

 of heavy, intractable yolk. 



2. From the fact that there are two sizes of eggs which 

 undergo slightly different modes of development it is concluded 

 that under normal conditions of growth sex is predetermined in 

 the egg. 



3. As far as the observations have been conducted the general 

 developmental history of the tadpole does not promise to afford 

 any very great assistance in deciding on the systematic position 

 of Anliydrophrync, but this is perhaps partly due to the fact 

 that the detailed comparative embryology of the different divisions 

 of the Anura is very incompletely known The general develop- 

 ment of Anhydrophryne is clearly much abbreviated, but in only 

 a few characters so far studied can the development be said to 

 be direct There is a well-developed tail, although it is never 

 used for swimming, while on the other hand there is a complete 

 absence of gills, gill-slits, suboral sucker and beak. 



4. Although the typical spiral intestifie of ordinary tadpoles 

 is never formed, and the gut is never greatly elongated, yet the 

 development of the gut is very far from being direct, for when 

 metamorphosis is proceeding and the tail is shrinking, every part 

 of the embryonic gut becomes modified to a surprising extent. 



* Witschi, Emil. — '' Development of Gonads and Ti'ansformation of Sex in 

 the Frog." Tlir American Nafiiralisf, Vol. LV, No. 641, p. 529, 1921. 



