PRODUCTION OF MONSTERS BY HYBRIDIZATION. 319 



very few hatch as perfectly normal larvae. A considerable per- 

 centage of embryos develop a circulation but have comparatively 

 small eyes as in Fig. I. Others have a proboscis and the eyes 

 both look forward as in Fig. 2. Still others have a very narrow 

 head with small eyes and the heart is a string-heart as in Fig. 3. 

 Others, finally, are cyclopic forms in which the mesio-lateral 

 development of the head has been more seriously inhibited than 

 the apico-basal (as in Fig. 4). 



The largest and most varied assemblage of monsters is found 

 in Class B in which the rate of cleavage was intermediate between 

 the lowest and highest rate. Types of embryos of this group 

 are shown in Figs. 5-12, which are camera lucida drawings made 

 when embryos were two weeks old. In all of these the whole 

 body from head to tail is abnormal (compare with the embryos 

 of A in which the tail is nearly normal). Ophthalmic terata are 

 most common here. Fig. 5 is microphthalmic and a little 

 asymmetrical and the body and tail are fairly normal; pectoral 

 fins are also developed and the otic vesicles are only slightly 

 enlarged. Fig. 9 has decidedly asymmetrical eyes, one very 

 small; the jaws, pectoral fins, etc., are also asymmetrical, but 

 the tail is fairly well developed. Fig. II shows a peculiar type 

 of stalked-eye, which is rather common; body is only slightly 

 abnormal; pectoral fins normal. Figs. 6 and 10 are two types of 

 cyclopic monster with reduced and shortened tail, but with 

 enlarged otic vesicles and good pectoral fins. Fig. 8 is a syn- 

 ophthalmic type with enlarged otic vesicles and much reduced 

 body. Fig. 12 is a common form with much reduced eyes, well 

 developed otic vesicles and small body. Fig. 7 is an eyeless 

 type in which the otic vesicles seem to have usurped the place 

 of the eyes in the body; the body is fairly well developed. All 

 of the types here shown had the heart beating. All of these 

 forms I look upon as products of acclimation after an early partial 

 inhibition. They were not as much retarded as those in lot C. 

 I look upon the enlargement of the otic vesicle as the result of 

 the suppression or partial suppression of the dominant region 

 anterior to it. The otic region now is to some extent physi- 

 ologically isolated and thus released to grow to a larger size than 

 normal. 



