Free-swimming Nauplius of Leptodora hyalina (Lilij.). 215 



The blood-corpuscles are large and frequently spherical. I think it 

 is probable that they are budded off from the compact mesoderm at 

 the posterior end of the body, but it is very difficult to be certain 

 about their origin. 



Fig. 5. — A. Obliquely transverse section through, the dorso-lateral swelling of a 

 nietanauplius. The maxillary gland has become sharply differentiated from 

 the imbedding octoderm. 



B. Similar section through an older metanauplius ; the space marked f has 

 developed. The space * will soon become continuous with the space around 

 the heart. 



In the earliest nauplius obtained the gonad is quite definitely 

 formed. Without doubt the generative cells originate exceedingly 

 early, probably they could have been distinguished in the blastosphere 

 stage as Grobben has described in the case of Moina. The ovary 

 becomes surrounded by a layer of mesoderm, and the generative duct 

 seems to be solely mesodermal. The main mass of the mesodermal 

 bands becomes converted into the characteristic double-layered fat- 

 body lying on each side of the gut. 



The origin of the antennary and maxillary glands has very con- 

 siderable morphological interest, and I have devoted much care in 

 endeavouring to elucidate it. The development of the maxillary gland 

 will be described first. 



On the lateral sides of the body of my youngest nauplius, just posterior 

 to the vertical plane passing through the second maxilla, the ectoderm 

 is several layers thick. This thickening is more pronounced dorsally, 

 and on surface view of the nauplius we can see a distinct dorso-lateral 



