236 SIDNEY F. HAEMER. 



Similarly the egg of Pyrosoma, like that of Salpa, makes 

 its appearance in the same precocious manner as thatof Crisia, 

 being formed very early from the so-called '^genital string" (Sa- 

 lensky, 29) . The early development, which is modified by the 

 presence of yolk, takes place in the interior of the old colony, 

 and is very abnormal, the blastomeres being for a time com- 

 pletely separated from one another (Salensky, p. 443). The 

 result of the development is the formation of the well-known 

 '' Cyathozooid," with its colony of four " Ascidiozooids," the 

 formation of which is compared by Salensky (30, p. 92) with 

 the embryonic fusion of Lumbricus trapezoides. The for- 

 mation of a stolon (represented by the chain of four Ascidio- 

 zooids) in the Pyrosoraa-embryo is further regarded as the 

 precocious acquirement by the embryo of the power of bud- 

 ding already possessed by the Synascidians. 



Peripatus^ is well known to be viviparous^ and the extra- 

 ordinary character of the segmentation of its ovum may have 

 some relation to the presence of external sources of nutriment. 



The cases already quoted may be taken as showing that 

 some of the abnormalities in the development of Crisia may 

 be due to the nutritive conditions in which the development 

 takes place. Just as the presence of food-yolk within the egg 

 modifies the character of the segmentation and of the forma- 

 tion of the layers, so the presence of copious stores of nutrient 

 material in the maternal tissues outside the egg may also affect 

 the early developmental processes. Thus the large number of 

 relatively large larvae which develop from the minute egg of a 

 Crisia could not be produced if the egg were not supplied 

 with nutriment from outside itself. While some of the irregu- 

 larity in the segmentation of the egg may be due to this cause, 

 the extreme independence of the blastomeres at an early stage 

 may be connected with the acquirement by the embryo of a 

 habit of forming buds in the embryonic condition. 



> See Sedgwick, No. 31. 



