214 ROBERT PAYNE BIGELOW ON 



tal muscles of the bud are derived from outgrowths of one or both of the septal muscles of 

 the parent which lie in the interradii adjoining the perradial area of bud formation. If tliis 

 be true, then every part of the young bud is formed from the corresponding j^art of the 

 parent, viz., — ectoderm from ectoderm, mesogloea from mesogloea, endoderm from endo- 

 derm, muscles from muscles, and digestive tract from digestive tract. There is no indica- 

 tion of any method of budding of the kind described by Lang ('92) . 



In the young bud the mesogloea is very thin, so that the ectoderm and endoderm are 

 very nearly in contact. The evagination gradually increases in size, becoming first hemi- 

 spherical and then more elongated. At the same time a constriction appears close to the 

 body of the scyphistoma, which deepens until the bud becomes a spindle-shaped body 

 attached to its parent by a short and narrow stem consisting of a film of mesogloea 

 covered with ectoderm, the digestive cavity of the bud being entirely closed (Fig. 1) . 



Scyphistomas are never found with more than two btids attached. When two buds 

 are present they are always of different ages, and the elder is always attached to the 

 apex of the younger (Fig. 2) . 



llic Planula-like Larva. — When finally constricted off, the bud is a simple, spindle- 

 shaped, hollow body, without trace of mouth or tentacles. It is like a planula in form and 

 habits. The whole surface is covered with cilia, and it swims about, rotating from right 

 to left upon its long axis. In swimming, the distal end is directed forward. While swim- 

 ming, the larva is constantly changing its shape, assuming in a few minutes various forms 

 from an elongated spindle to a short heart-shape (Fig. 3, ^4, B and C) . It swims near 

 the bottom, hiding under any object that it may find there. When it strikes an 

 obstacle, it may rest there quietly, or it may rotate slowly upon its long axis. In all 

 its movements it reminds one very strongly of Agassiz's description of the planulae 

 of Aurelia. 



The larva is white, sj^eckled with a few greenish l)rown spots. It is rather opaqvxe, 

 but much of the structure may be seen in a living specimen. A longitudinal section shows 

 that the ectoderm consists of a deep layer of very narrow and closely-packed columnar 

 cells (Fig. 39) . The mesogloea contains a few green cells (producing the greenish brown 

 spots) , and some widely scattered coUoblasts. The layer is thickest at the equator, 

 diminishing gradually to a very thin layer at both ends. The four septal muscles [sni) 

 are seen clearly at the distal end of the larva, embedded in the mesogloea and united with 

 the ectoderm near the apex (Fig. 38). In one specimen, not yet detached from the 

 parent, it was possible to trace one of the muscles all the way from the proximal to the 

 distal end. The muscle fibres are already differentiated and line the tube of mesogloea, 

 while the nuclei occupy a central position. 



The endoderm is a columnar epithelium, rather thin, with the cells closely packed 



